Regio- and stereoselective carbometallation reactions of N-alkynylamides and sulfonamides

• Yury Minko,
• Morgane Pasco,
• Helena Chechik and
• Ilan Marek

Beilstein J. Org. Chem. 2013, 9, 526–532, doi:10.3762/bjoc.9.57

• preformed organocopper species (Table 2, entries 7–10) [25]. Carbocupration of cyclic N-alkynylcarbamate (chiral oxazolidinone moiety) Recently, our group was particularly interested in the carbometallation reaction of ynamides bearing chiral cyclic carbamates 7, particularly the Evans's oxazolidinone [27

• carbocupration reaction is again at the center of interest but this time for the regioselective addition of organocopper derivatives to various ynamide species. Particularly interesting is the carbocupration of N-alkynyl carbamates 7, bearing Evans’s oxazolidinone chiral auxiliary, which leads to the formation

Inter- and intramolecular enantioselective carbolithiation reactions

• Asier Gómez-SanJuan,
• Nuria Sotomayor and
• Esther Lete

Beilstein J. Org. Chem. 2013, 9, 313–322, doi:10.3762/bjoc.9.36

• synthesis of chiral aromatics and heteroaromatics, such as isoquinolines or benzofurans, though lower yields and ee were obtained [15]. On the other hand, α-aryl O-(α-arylalkenyl) carbamates (α-carbamoyloxy-substituted styrenes) such as 14 undergo facile intermolecular carbolithiation reactions, via

• secondary α-carbamoyloxybenzyllithiums 15, in the presence of chiral diamines, such as (−)-sparteine (L1) or (−)-α-isosparteine (L3), but only with moderate enantiofacial differentiation. The best results are obtained with unsubstituted alkenes (vinyl carbamates) by using butyllithium/(−)-α-isosparteine (up

• , the first examples reported of asymmetric intramolecular carbolithiation reactions using alkyllithiums took advantage of the (−)-sparteine-mediated enantioselective deprotonation reaction of carbamates [39]. Thus, achiral (Z)- or (E)-6-phenyl-hex-5-enylcarbamates 25 can be cyclized with sec

trans-2-(2,5-Dimethoxy-4-iodophenyl)cyclopropylamine and trans-2-(2,5-dimethoxy-4-bromophenyl)cyclopropylamine as potent agonists for the 5-HT₂ receptor family

• Adam Pigott,
• Stewart Frescas,
• John D. McCorvy,
• Xi-Ping Huang,
• Bryan L. Roth and
• David E. Nichols

Beilstein J. Org. Chem. 2012, 8, 1705–1709, doi:10.3762/bjoc.8.194

• carbamates 11a and 11b (Scheme 2). A brief treatment of these with 3 M HCl at 45 °C cleanly affected N-deprotection and afforded the desired final amines 4 and 5. The stereochemistry of the more potent enantiomer of DOI is (−)-(R) [7], and of 3 is (−)-(1R,2S) [2]. We therefore undertook the resolution of the

The Amadori rearrangement as glycoconjugation method: Synthesis of non-natural C-glycosyl type glycoconjugates

• Katharina Gallas,
• Gerit Pototschnig,
• Florian Adanitsch,
• Arnold E. Stütz and
• Tanja M. Wrodnigg

Beilstein J. Org. Chem. 2012, 8, 1619–1629, doi:10.3762/bjoc.8.185

• ) gave the corresponding 1-N,2-O-cyclic carbamates in 95% yield with a 3:2 ratio of the pyranoid 26a and furanoid 26b forms, and compounds 25 (a and b) reacted accordingly and gave cyclic carbamates 27a and 27b in a 5:3 ratio and a combined yield of 50%. In the D-manno series, the C-elongation employing

• -dioxane as co-solvent (1 mL). When TLC indicated complete consumption of the starting material, the solvents were removed under reduced pressure, and silica-gel chromatography (CHCl3/MeOH 6:1 v/v containing 1% of concd NH4OH) gave a mixture of cyclic carbamates in the pyranoid 27a and furanoid 27b form in

Automated synthesis of sialylated oligosaccharides

• Davide Esposito,
• Mattan Hurevich,
• Bastien Castagner,
• Cheng-Chung Wang and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2012, 8, 1601–1609, doi:10.3762/bjoc.8.183

• carbamates has to be performed manually at the end of an automated sequence. These features make the automated platform very attractive for sialoside synthesis. Based on the encouraging results obtained for the solution-phase synthesis of 16, building blocks 4 and 5 were used for the automated solid-phase

Approaches to α-amino acids via rearrangement to electron-deficient nitrogen: Beckmann and Hofmann rearrangements of appropriate carboxyl-protected substrates

• Sosale Chandrasekhar and
• V. Mohana Rao

Beilstein J. Org. Chem. 2012, 8, 1393–1399, doi:10.3762/bjoc.8.161

• corresponding methyl carbamates 10 were obtained in excellent yields (Table 3). The reaction may well occur via the putative N-acetoxy derivative I (up to now this has not been proven). The in situ trapping of the expected isocyanate intermediate (not shown) by methanol would explain the final formation of 10

• . All products were generally purified chromatographically and fully characterized spectroscopically (including HRMS). In addition, two of the final carbamates (10a and 10b) were confirmed by X-ray diffraction analysis (Figure 2 and Table 4) [24]. The carbamates 10 apparently evidenced restricted

• rotation around the amide C–N moiety (partial double-bond character) in the NMR as seen by twin peaks in certain cases [25]. In carbamates 10, the substitution pattern α to the C=O group in 7–9 has shifted to the α-position next to the amino center. Therefore, in this strategy (Scheme 2) the enolate

Carbamate derivatives and sesquiterpenoids from the South China Sea gorgonian Melitodes squamata

• Li-Si Huang,
• Fei He,
• Hui Huang,
• Xiao-Yong Zhang and
• Shu-Hua Qi

Beilstein J. Org. Chem. 2012, 8, 170–176, doi:10.3762/bjoc.8.18

• amidation position of the two molecules of 4. Based on the 1H NMR, 13C NMR HSQC, HMBC and 1H–1H COSY spectral data analysis, the structure of 2 was elucidated to be as shown above and named as obtucarbamate D. Urea derivatives are closely related in structure to carbamates. Urea is synthesized in the body

Multistep flow synthesis of vinyl azides and their use in the copper-catalyzed Huisgen-type cycloaddition under inductive-heating conditions

• Lukas Kupracz,
• Jan Hartwig,
• Jens Wegner,
• Sascha Ceylan and
• Andreas Kirschning

Beilstein J. Org. Chem. 2011, 7, 1441–1448, doi:10.3762/bjoc.7.168

• (IN3, 1). In their synthesis of carbamates Wirth and coworkers [10] recently showed that some of the practical problems associated with iodine azide can be circumvented or minimized by generating and immediately consuming iodine azide under flow conditions. Because of low yields, this ingenious process

Amines as key building blocks in Pd-assisted multicomponent processes

• Didier Bouyssi,
• Nuno Monteiro and
• Geneviève Balme

Beilstein J. Org. Chem. 2011, 7, 1387–1406, doi:10.3762/bjoc.7.163

• ]. Various chloroformates and imines can participate in this reaction, stannanes being limited to aryl, benzyl or ethyl ones. When vinylstannane was used, the transmetallation step was more rapid than the CO insertion, giving instead substituted carbamates. After removal of the solvents in vacuo, the

Carbamate-directed benzylic lithiation for the diastereo- and enantioselective synthesis of diaryl ether atropisomers

• Abigail Page and
• Jonathan Clayden

Beilstein J. Org. Chem. 2011, 7, 1327–1333, doi:10.3762/bjoc.7.156

• assign absolute or relative stereochemistry in this work. However, a few reasonable assumptions allow us to propose likely assignments, and these are the ones used in the structural diagrams in this paper: 1. (−)-Sparteine favours deprotonation of the pro-S proton of carbamates. Invertive quench would

Meta-metallation of N,N-dimethylaniline: Contrasting direct sodium-mediated zincation with indirect sodiation-dialkylzinc co-complexation

• David R. Armstrong,
• Liam Balloch,
• Eva Hevia,
• Alan R. Kennedy,
• Robert E. Mulvey,
• Charles T. O'Hara and
• Stuart D. Robertson

Beilstein J. Org. Chem. 2011, 7, 1234–1248, doi:10.3762/bjoc.7.144

• and Discussion The original direct meta-zincation reaction. In comparison to tertiary amides and O-carbamates, anilines are relatively modest metallation directing groups [19][29]. Activation of N,N-dimethylaniline transpires primarily from the acidifying effect of the N atom; the coordination effect

Triazole–Au(I) complex as chemoselective catalyst in promoting propargyl ester rearrangements

• Dawei Wang,
• Yanwei Zhang,
• Rong Cai and
• Xiaodong Shi

Beilstein J. Org. Chem. 2011, 7, 1014–1020, doi:10.3762/bjoc.7.115

• products were obtained in excellent yields (generally >90% yields with 1% loading). Besides the typical ester migrating groups, carbonates and carbamates were also found to be suitable for this transformation, which provided a highly efficient, practical method for the preparation of substituted allenes

• summarized in Table 2. As indicated in Table 2, carbonates (entries 1–5) and carbamate (entry 6) were also suitable for this transformation. Compared to the allene-acetates, the allene-carbonates and allene-carbamates were more stable in water. Notably, although the alkene was considered as a readily

• application of the allene-carbonates and allene-carbamates as building blocks for development of new synthetic methodologies is currently underway in our group. Chemoselective activation of alkyne over allene by the TA–Au catalysts. The counter ligands, an important factor in Au(I) catalysis. The challenge of

A practical route to tertiary diarylmethylamides or -carbamates from imines, organozinc reagents and acyl chlorides or chloroformates

• Erwan Le Gall,
• Antoine Pignon and
• Thierry Martens

Beilstein J. Org. Chem. 2011, 7, 997–1002, doi:10.3762/bjoc.7.112

• -carbamates from imines, organozinc reagents and acyl chlorides or chloroformates is described. This route involves the formation of an imine, which is used without isolation, followed by its activation by the carbonyl-containing electrophile and the trapping of the acyliminium by an organozinc reagent. Most

• steps are conducted concomitantly to render the procedure as practical and straightforward as possible. Therefore, the whole experimental protocol takes less than two hours. Keywords: acyliminium; amides; carbamates; multicomponent reactions; organozinc reagents; Introduction Diarylmethylamines

• constitute an important class of nitrogen-containing compounds displaying antihistaminic, anti-arrhythmic, diuretic, antidepressant, laxative, anesthetic and anticholinergic properties [1][2]. In this context, diarylmethylamides and -carbamates represent reliable N-protected diarylmethylamine derivatives and

Asymmetric synthesis of tertiary thiols and thioethers

• Jonathan Clayden and
• Paul MacLellan

Beilstein J. Org. Chem. 2011, 7, 582–595, doi:10.3762/bjoc.7.68

• an intramolecular aryl transfer. Treatment of an N-aryl S-benzyl thiocarbamate 92 leads to formation of a lithio derivative 93 comparable with those reported by Hoppe (Scheme 32). As in the case of lithiated N-aryl ureas [76][77][78][79][80] and N-aryl carbamates [81][82], the N-aryl ring is

• contrast to the rearrangement of lithiated carbamates [81][82]), aryl migration proceeds with retention of stereochemistry. Current work is continuing with the aim of expanding the utility of this new mode of reactivity displayed by thiocarbamates. Conclusion Of the methods available for the synthesis of

Palladium-catalyzed formation of oxazolidinones from biscarbamates: a mechanistic study

• Benan Kilbas and
• Metin Balci

Beilstein J. Org. Chem. 2011, 7, 246–253, doi:10.3762/bjoc.7.33

• product (Scheme 6). In the case of 8, 16 and 19, the leaving groups, carbamates, are in anti (referred to the cyclopropane ring) positions and, therefore, the palladium complex should approach the double bond in 8, 16, and 19 from the side of the three-membered ring to form a complex. However, the

Synthesis and self-assembly of 1-deoxyglucose derivatives as low molecular weight organogelators

• Guijun Wang,
• Hao Yang,
• Sherwin Cheuk and
• Sherman Coleman

Beilstein J. Org. Chem. 2011, 7, 234–242, doi:10.3762/bjoc.7.31

• series of methyl 4,6-O-benzylidene-α-D-glucopyranoside (1) derivatives (Figure 1), including esters and carbamates with different functional groups. Several of these compounds proved to be effective gelators for organic solvents and aqueous solutions [34][35][36][37]. We found that the structures of the

Palladium- and copper-mediated N-aryl bond formation reactions for the synthesis of biological active compounds

• Carolin Fischer and
• Burkhard Koenig

Beilstein J. Org. Chem. 2011, 7, 59–74, doi:10.3762/bjoc.7.10

• , carbamates, N-heterocycles, enamines and intramolecular N-arylation reactions [45]. We compare here the success of the different C–N-arylation reactions as applied to the synthesis of more complex structures and discuss selected examples of palladium- and copper-mediated reactions for the synthesis of

Recent advances in carbocupration of α-heterosubstituted alkynes

• Ahmad Basheer and
• Ilan Marek

Beilstein J. Org. Chem. 2010, 6, No. 77, doi:10.3762/bjoc.6.77

• combined with its strong ability to coordinate organometallic derivatives have a major directing effect and favor formation of the α-isomer (Scheme 7) [19]. Thus, when alkynyl carbamates 12a,b are added to organocopper derivatives RCu•MgBr2 in Et2O at −78 °C for only 90 min, the expected linear products 13

• stereospecifically the trisubstituted enol carbamates as single isomers. It is important to note that the nature of solvent plays a critical role in the regioselectivity of this reaction. Diethyl ether leads to the linear product, whereas THF gives the branched product as the major reaction product (branched/linear

• N-substituted alkynes give the β-isomer due to the mesomeric effect of the heteroatom, except when an extra chelating moiety is present such as in alkynyl-O-carbamates, THPoxy-alkynes, and ynamides. In these cases, the opposite α-isomers are formed. P-, S- and Si-substituted alkynes all give the α

(Pseudo)amide-linked oligosaccharide mimetics: molecular recognition and supramolecular properties

• José L. Jiménez Blanco,
• Fernando Ortega-Caballero,
• Carmen Ortiz Mellet and
• José M. García Fernández

Beilstein J. Org. Chem. 2010, 6, No. 20, doi:10.3762/bjoc.6.20

• activities, probably due to the presence of a hydrophilic sugar substituent at the nitrogen atom of the nor-tropane ring [71][72]. Several groups have shown that disaccharide ureas and carbamates with different bridging positions as α/β-anomers are readily accessible by the coupling reaction of aminosugars

2-Phenyl- tetrahydropyrimidine- 4(1H)-ones – cyclic benzaldehyde aminals as precursors for functionalised β²-amino acids

• Markus Nahrwold,
• Arvydas Stončius,
• Anna Penner,
• Beate Neumann,
• Hans-Georg Stammler and
• Norbert Sewald

Beilstein J. Org. Chem. 2009, 5, No. 43, doi:10.3762/bjoc.5.43

• containing e.g. tert-butyl protected side chain functions. Amino acids protected like that are particularly suitable for solid phase peptide synthesis and are thus highly desirable. Our novel ring cleavage concept includes the protection of both ring-nitrogen atoms as carbamates (Scheme 1C). Similar to the

Convenient method for preparing benzyl ethers and esters using 2-benzyloxypyridine

• Susana S. Lopez and
• Gregory B. Dudley

Beilstein J. Org. Chem. 2008, 4, No. 44, doi:10.3762/bjoc.4.44

• (entry 7, 84%) and methyl lactate (3e, 79%) verify compatibility with esters and carbamates. Note that the benzylation of N-Boc-serine methyl ester (3d) compares favourably to analogous reactions reported previously [24], because the neutral reaction conditions described herein are compatible with the

Vinylogous Mukaiyama aldol reactions with 4-oxy-2-trimethylsilyloxypyrroles: relevance to castanospermine synthesis

• Roger Hunter,
• Sophie C. M. Rees-Jones and
• Hong Su

Beilstein J. Org. Chem. 2007, 3, No. 38, doi:10.1186/1860-5397-3-38

• doubt. Attention was then turned to changing the N-protecting group to a carbamate in line with TBSOP 1. The pyrroline precursor 4 (R1 = H, R2 = OMe) was readily prepared via condensation of ethyl E-4-chloro-3-methoxybut-2-enoate with ammonia, and then transformed to carbamates 4c and 4d under the

• pyrrolinone with formation of a multitude of products. This was attributed to the instability of the pyrrolinone carbamates 4c and 4d towards n-BuLi, and indicated the need to resort to the Casiraghi conditions of 2,6-lutidine and TBSOTf for silyloxypyrrole generation.[12] However, in view of our objective of

An asymmetric synthesis of all stereoisomers of piclavines A1-4 using an iterative asymmetric dihydroxylation

• Yukako Saito,
• Naoki Okamoto and
• Hiroki Takahata

Beilstein J. Org. Chem. 2007, 3, No. 37, doi:10.1186/1860-5397-3-37

• clean deprotection of Cbz. However, treatment of (2R-[4S])-16 with iodotrimethylsilane (TMSI)[13] in CH3CN provided the amine (75%), which was treated with TrocCl/K2CO3 to afford the Troc carbamates (2R-[4S])-17. After mesylation of [2S-(4R)]-17, N-deprotection of the resulting mesylate with 10% Cd-Pb

The oxanorbornene approach to 3-hydroxy, 3,4-dihydroxy and 3,4,5-trihydroxy derivatives of 2-aminocyclohexanecarboxylic acid

• Ishmael B. Masesane,
• Andrei S. Batsanov,
• Judith A. K. Howard,
• Raju Mondal and
• Patrick G. Steel

Beilstein J. Org. Chem. 2006, 2, No. 9, doi:10.1186/1860-5397-2-9

• carbamates we then sort to exploit the alkene units to provide a convenient source of poly-hydroxylated cyclohexane β-aminoacids. Consequently, treatment of endo derived hydroxy diene with mCPBA in DCM afforded a separable 9:1 mixture of epoxides 10 and 11 favouring addition syn to the carbamate, Scheme 3

• reaction. Concurring with our results, Donohoe has reported that cyclic homoallylic carbamates give high levels of syn selectivity in the OsO4 mediated dihydroxylation reactions.[25][26] On the other hand, Kishi has established that the OsO4 mediated oxidation of cyclic allylic alcohols led preferentially

Total syntheses of oxygenated brazanquinones via regioselective homologous anionic Fries rearrangement of benzylic O-carbamates

• Glaucia Barbosa Candido Alves Slana,
• Mariângela Soares de Azevedo,
• Rosângela Sabattini Capella Lopes,
• Cláudio Cerqueira Lopes and
• Jari Nobrega Cardoso

Beilstein J. Org. Chem. 2006, 2, No. 1, doi:10.1186/1860-5397-2-1

• new variations of anionic aromatic chemistry, the total synthesis of oxygenated brazanquinones (1a-1c), derived from β-brasan, a natural product isolated from Caesalpina echinata, via carbamates 2a-2c is described. Introduction The search for new synthetic routes for the total synthesis of

• -diethylcarbamoyl chloride, and sodium hydride afforded the carbamates 2a-2d (Scheme 2). The carbamates 2a-2c were cyclized in the presence of excess sec-BuLi in THF at -78°C to afford the desired brazanquinones 1a-1c in reasonable yields (54%–57%) (Scheme 2). The mechanism suggested by us and shown in Scheme 1

• , involves first the preparation of aryllithium intermediates 3 from the carbamates 2a-2b by the reversible metathesis reaction known [21][22][23] as the lithium-halogen exchange which has been widely employed for replacement of a bromine or iodine atom in a substrate by lithium. The intermediate 3 then