Phosphinate-containing heterocycles: A mini-review

• Olivier Berger and
• Jean-Luc Montchamp

Beilstein J. Org. Chem. 2014, 10, 732–740, doi:10.3762/bjoc.10.67

• cyclization through conjugate addition of ethyl 7-(ethoxy-H-phosphinoyl)-3-methyl-2-heptenoate (48) in the presence of potassium tert-butoxide (Scheme 20) [28]. A phosphorino[3’,4’:4,5]furo[2,3-d]-1,3-dioxole 51 was synthesized in 36% yield by Tattersall and coworkers by realizing a double Arbuzov-type

Carbenoid-mediated nucleophilic “hydrolysis” of 2-(dichloromethylidene)-1,1,3,3-tetramethylindane with DMSO participation, affording access to one-sidedly overcrowded ketone and bromoalkene descendants^§

• Rudolf Knorr,
• Thomas Menke,
• Johannes Freudenreich and
• Claudio Pires

Beilstein J. Org. Chem. 2014, 10, 307–315, doi:10.3762/bjoc.10.28

• polar solvents. In DMSO with potassium tert-butoxide (KOt-Bu, four equiv, >22 hours at 140 °C) or better with solid KOH (at least 29 equiv, ≥ six hours at 100 °C or 60 min at 154 °C), however, 6 was slowly transformed into 10. This may be reminiscent of a 109-fold increased kinetic basicity [19][20] of

Substrate dependent reaction channels of the Wolff–Kishner reduction reaction: A theoretical study

• Shinichi Yamabe,
• Guixiang Zeng,
• Wei Guan and
• Shigeyoshi Sakaki

Beilstein J. Org. Chem. 2014, 10, 259–270, doi:10.3762/bjoc.10.21

• (Ph)2 in 85% yield from benzophenone hydrazone Ph2C=N–NH2 and potassium tert-butoxide KOt-Bu in DMSO [10]. Grundon et al. obtained the product also in 85% yield in toluene [11]. These non-aqueous experimental results indicate that the tert-butoxide ion directly participates in the proton shifts. As a

Synthesis of five- and six-membered cyclic organic peroxides: Key transformations into peroxide ring-retaining products

• Alexander O. Terent'ev,
• Dmitry A. Borisov,
• Vera A. Vil’ and
• Valery M. Dembitsky

Beilstein J. Org. Chem. 2014, 10, 34–114, doi:10.3762/bjoc.10.6

• also be synthesized via the ozonolysis of alkene 248 in the presence of hydrogen peroxide followed by the cyclization of bis(hydroperoxide) 249 with potassium tert-butoxide (Scheme 71) [252]. An approach to the cyclization based on an intramolecular nucleophilic substitution was used also for the

• synthesis of diastereomers of dioxanes 252a,b containing triple bonds. Hydroperoxides 251a,b that were synthesized by the ozonolysis of 250 were treated with potassium tert-butoxide. One of the diastereomers, 252a, was then modified first via the stereoselective hydrozirconation and iodination to 253a and

Anionic cascade reactions. One-pot assembly of (Z)-chloro-exo-methylenetetrahydrofurans from β-hydroxyketones

• István E. Markó and
• Florian T. Schevenels

Beilstein J. Org. Chem. 2013, 9, 1319–1325, doi:10.3762/bjoc.9.148

• , possessing unique structural features. Keywords: acetylene addition; dichloroethylene; dimerisation; dioxanes; tetrahydrofurans; Introduction Recently, we have shown that simple ketones reacted with 1,1-dichloroethylene, in the presence of potassium tert-butoxide, to afford rare (Z)-chloro-exo

• lithium chloroacetylide, generated in situ from dichloroethylene and LDA, the diol 12 was obtained in 77% yield. This adduct smoothly cyclized to 13 upon addition of sodium or potassium tert-butoxide, thereby supporting our mechanistic proposal. Repeating the process without isolation of the intermediate

• diol 12 proved to be even more efficient, affording the (Z)-chloro-exo-methylenetetrahydrofuran 13 in 66% overall yield (Scheme 3). It is interesting to note that, in the case of the substrate 11, the adduct 13 could be isolated in an improved 81% yield when potassium tert-butoxide was employed as the

A new synthetic protocol for coumarin amino acid

• Xinyi Xu,
• Xiaosong Hu and
• Jiangyun Wang

Beilstein J. Org. Chem. 2013, 9, 254–259, doi:10.3762/bjoc.9.30

• to 5c, respectively, if sodium hydride was used). In the presence of potassium tert-butoxide and a catalytic amount of tetrabutylammonium bromide, alkene 5 reacted with diethyl acetamidomalonate (DEAM) [13] to form malonate 6 in high yield (6a, 73.1% yield; 6b, 86.0%; 6c, 86.0%). It was then heated

• yield was investigated (Table 1). Three different bases including sodium hydride, 1,8-diazabicycloundec-7-ene (DBU) and potassium tert-butoxide (KOt-Bu) were used, and the reactions were carried out at 25 °C for 5 h. DBU gave the best yield in the synthesis of 5a, 5b or 5c, whereas there was no reaction

Highly stereocontrolled synthesis of trans-enediynes via carbocupration of fluoroalkylated diynes

• Tsutomu Konno,
• Misato Kishi and
• Takashi Ishihara

Beilstein J. Org. Chem. 2012, 8, 2207–2213, doi:10.3762/bjoc.8.249

• 1.5 equiv of potassium tert-butoxide (t-BuOK) in THF at room temperature for 2 h. Very surprisingly, the desired trifluoromethylated diyne 4a was not detected at all and the addition–elimination product 5a was obtained quantitatively. Therefore, we examined the reaction conditions for the β

Engineering of indole-based tethered biheterocyclic alkaloid meridianin into β-carboline-derived tetracyclic polyheterocycles via amino functionalization/6-endo cationic π-cyclization

• Piyush K. Agarwal,
• Meena D. Dathi,
• Mohammad Saifuddin and
• Bijoy Kundu

Beilstein J. Org. Chem. 2012, 8, 1901–1908, doi:10.3762/bjoc.8.220

• [61]. Next, 1H-benzo[d][1,2,3]triazol-1-yl-(1-methyl-1H-indol-3-yl)methanone (4a) was converted into its α-nitroketone 5a by treating with nitromethane in the presence of potassium tert-butoxide in DMSO [62]. 1-(1-Methyl-1H-indol-3-yl)-2-nitroethanone (5a) was reacted with N,N-dimethylformamide

• potassium tert-butoxide in DMSO. Reaction of 15 with N,N-dimethylformamide dimethyl acetal provided 16, which was cyclized in the presence of guanidine hydrochloride and N,N-dimethylguanidine sulfate to give the nitro products 17a,b and 17c. Finally, the desired substrates 18 were obtained by reducing 17

Automated three-component synthesis of a library of γ-lactams

• Erik Fenster,
• David Hill,
• Oliver Reiser and
• Jeffrey Aubé

Beilstein J. Org. Chem. 2012, 8, 1804–1813, doi:10.3762/bjoc.8.206

• produced 3{1,1} in high yields and with high enantioselectivity, albeit with low diastereoselectivity. Such a low diastereoselectivity was of no concern in the originally reported procedure since the final potassium tert-butoxide promoted epimerization step produced a racemic mixture of a single

• (Table 2, entry 1) or reaction times (Table 2, entry 2) seemed to indicate that the lactamization in forming the syn-diastereomer of 6{1,1,1} occurs at a slower rate than that for the anti-diastereomer. However, we found that subjecting succinimide 7{1,1,1} by itself to potassium tert-butoxide in

• and epimerization steps were combined. Thus, subjecting 3{1,1,1} to the reductive amination conditions for 2 h at room temperature, followed by addition of potassium tert-butoxide (after a solvent change from CHCl3 to MeOH) provided the γ-lactam 6{1,1,1} in 81% (Scheme 3) [15]. Having demonstrated the

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

• derivatives 7 were formed in excellent yields (Table 3). The α-alkyl derivatives 7 were hydrolyzed with potassium tert-butoxide and water in ether [20], the corresponding acids 8 being obtained in excellent yields (Table 3). Conventional hydrolysis with aqueous KOH was unsuccessful, probably for steric

Organocatalytic C–H activation reactions

• Subhas Chandra Pan

Beilstein J. Org. Chem. 2012, 8, 1374–1384, doi:10.3762/bjoc.8.159

• , potassium tert-butoxide (1.0 equiv) and DMEDA (N,N’-dimethylethane-1,2-diamine) were found to be the best base and catalyst, respectively, providing the desired product 20 in 84% yield (Scheme 14). It is remarkable that cis-cyclohexane-1,2-diol is also a good catalyst for this reaction (81% yield). Under

• under the same reaction conditions. Shi and co-workers reported a similar reaction with 1,10-phenanthroline as catalyst at 100 °C employing aryl iodides and aryl bromides as the substrates [34]. Whereas 40 mol % of the catalyst and 3.0 equivalents of potassium tert-butoxide as base were needed for the

• reaction with bromides, 20 mol % of the catalyst and 2.0 equivalents of potassium tert-butoxide were required for the reaction with iodides. Under these optimized conditions, different aryl bromides and aryl iodides were screened, and poor to good yields (27–89%) for the products 20 were observed (Scheme

Algicidal lactones from the marine Roseobacter clade bacterium Ruegeria pomeroyi

• Ramona Riclea,
• Julia Gleitzmann,
• Hilke Bruns,
• Corina Junker,
• Barbara Schulz and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2012, 8, 941–950, doi:10.3762/bjoc.8.106

• hydrogenation was carried out in a H2 atmosphere (1 bar) at 20 °C for 24 h. The reaction mixture was filtered through silica gel and concentrated to yield (2R,4S)-7. The product was used in the next step without purification. Treatment of (2R,4S)-7 with potassium tert-butoxide (5 mg) in tert-butanol (1 mL

Alkoxide-induced ring opening of bicyclic 2-vinylcyclobutanones: A convenient synthesis of 2-vinyl-substituted 3-cycloalkene-1-carboxylic acid esters

• Xiufang Ji,
• Zhiming Li,
• Quanrui Wang and
• Andreas Goeke

Beilstein J. Org. Chem. 2012, 8, 650–657, doi:10.3762/bjoc.8.72

• alpha position can be achieved by the action of sodium methoxide or potassium tert-butoxide. This approach constitutes an efficient path to vicinally disubstituted ester products 5 or 6. Results and Discussion We began our investigation with the preparation of cyclobutanones as shown in Scheme 2. The

• substrate with sodium methoxide or potassium tert-butoxide as the base. Various reaction conditions, including the amount of metal alkoxide, solvents and reaction temperature were examined. Representative results are listed in Table 2. It was found that both MeONa and t-BuOK can promote the ring opening to

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

• the azide anion onto the intermediate iodo azide. Next, we studied the elimination step that should yield the target vinyl azides. Hassner et al. [9] relied on potassium tert-butoxide as a base, which indeed worked well in diethyl ether as the solvent in our initial batch experiments (Table 2, entry 1

Intraannular photoreactions in pseudo-geminally substituted [2.2]paracyclophanes

• Henning Hopf,
• Vitaly Raev and
• Peter G. Jones

Beilstein J. Org. Chem. 2011, 7, 658–667, doi:10.3762/bjoc.7.78

• , 137.2, 135.5 (+), 134.6 (+), 132.4 (+), 129.8 (+), 114.6 (−), 35.0 (−), 32.5 (−) ppm; MS (EI, 70 eV) m/z (%): 261 (8), 260 (34), 131 (36), 130 (39), 129 (100), 128 (24), 115 (34). 4,15-bis(butadien-1-yl)[2.2]paracyclophane (11): A freshly prepared solution of potassium tert-butoxide (2.69 g, 24.0 mmol

• /z (%): 312 (20), 157 (31), 156 (42), 155 (100), 142 (11), 141 (58), 129 (16), 128 (25), 115 (14). 4,15-Bis[(Z)-2-cyclopropylvinyl][2.2]paracyclophane (22): A freshly prepared solution of potassium tert-butoxide (898 mg, 8.0 mmol) in anhydrous THF (30 mL) was added dropwise over 30 min to a cooled

• ; methyltriphenylphosphonium bromide was purchased from Acros. Reagents were used without further purification. Solvents used were of analytical grade; anhydrous THF was distilled from an LiAlH4 dispersion with triphenylmethane as indicator. 4,15-Divinyl[2.2]paracyclophane (7): A freshly prepared solution of potassium tert

Synthesis of 5-(2-methoxy-1-naphthyl)- and 5-[2-(methoxymethyl)-1-naphthyl]-11H-benzo[b]fluorene as 2,2'-disubstituted 1,1'-binaphthyls via benzannulated enyne–allenes

• Yu-Hsuan Wang,
• Joshua F. Bailey,
• Jeffrey L. Petersen and
• Kung K. Wang

Beilstein J. Org. Chem. 2011, 7, 496–502, doi:10.3762/bjoc.7.58

• synthesized by treatment of the corresponding benzannulated enediynes with potassium tert-butoxide in refluxing toluene to give benzannulated enyne–allenes for the subsequent Schmittel cascade cyclization reactions. The structures of these two 5-(1-naphthyl)-11H-benzo[b]fluorenes could be regarded as 2,2

• enediynes. Specifically, treatment of the benzannulated enediyne 1a with potassium tert-butoxide in refluxing toluene for six hours promoted a 1,3-prototropic rearrangement to produce, in situ, the benzannulated enyne–allene 2a, which in turn underwent a sequence of Schmittel cascade cyclization reactions

• -ethynyl-2-(methoxymethyl)benzene (4b). On exposure to potassium tert-butoxide in refluxing toluene for five hours, 9a was transformed to 5-(2-methoxyphenyl)-11H-benzo[b]fluorene 13a along with a small amount (ca. 2%) of 14a in a single operation. Presumably, the cascade sequence involved an initial 1,3

Pd-catalyzed decarboxylative Heck vinylation of 2-nitrobenzoates in the presence of CuF₂

• Lukas J. Gooßen,
• Bettina Zimmermann and
• Thomas Knauber

Beilstein J. Org. Chem. 2010, 6, No. 43, doi:10.3762/bjoc.6.43

• tert-butoxide (2.24 g, 20 mmol) in ethanol (20 mL) was added dropwise over 2 h. After complete addition, the reaction mixture was stirred for a further 1 h at room temperature. The gradual formation of a white precipitate was observed. The resulting solid was collected by filtration through a 7-cm

• Combi Flash Companion-Chromatography-System (Isco-Systems) and RediSep packed columns (12 g). General procedure for the synthesis of the potassium carboxylates A 250 mL, two-necked, round-bottomed flask was charged with the carboxylic acid (20 mmol) and ethanol (20 mL). To this, a solution of potassium

Efficient and improved synthesis of Telmisartan

• A. Sanjeev Kumar,
• Samir Ghosh and
• G. N. Mehta

Beilstein J. Org. Chem. 2010, 6, No. 25, doi:10.3762/bjoc.6.25

• , Telmisartan (1) in 21% overall yield and with eight steps as the longest sequence [5]. Several improvements to the above reaction sequence have been reported, e.g., the use of KOH instead of potassium tert-butoxide in the penultimate step and the use of methanolic HCl solution instead of trifluoroacetic acid

Synthesis and Diels–Alder cycloaddition reaction of norbornadiene and benzonorbornadiene dimers

• Bilal Nişancı,
• Erdin Dalkılıç,
• Murat Güney and
• Arif Daştan

Beilstein J. Org. Chem. 2009, 5, No. 39, doi:10.3762/bjoc.5.39

• dibromides 3 with potassium tert-butoxide resulted in the formation of monobromide 4. The other starting material 5 was obtained using the reported procedures based on the use of potassium tert-butoxide/n-butyllithium super-base by starting with commercially available norbornadiene [24][25][26][27]. When 2

Trifluoromethyl ethers – synthesis and properties of an unusual substituent

• Frédéric R. Leroux,
• Baptiste Manteau,
• Jean-Pierre Vors and
• Sergiy Pazenok

Beilstein J. Org. Chem. 2008, 4, No. 13, doi:10.3762/bjoc.4.13

• potassium tert-butoxide (KOR) in tetrahydrofuran at −100 °C. Upon trapping with molecular iodine, 3-iodo-4-trifluoromethoxybiphenyl was isolated in 90% yield [73]. Under the same conditions as employed with trifluoromethoxybenzene, 1- and 2-trifluoromethoxynaphthalene undergo selective lithiation at the 2

Analogues of amphibian alkaloids: total synthesis of (5R,8S,8aS)-(−)-8-methyl- 5-pentyloctahydroindolizine (8-epi-indolizidine 209B) and [(1S,4R,9aS)-(−)-4-pentyloctahydro- 2H-quinolizin- 1-yl]methanol

• Joseph P. Michael,
• Claudia Accone,
• Charles B. de Koning and
• Christiaan W. van der Westhuyzen

Beilstein J. Org. Chem. 2008, 4, No. 5, doi:10.1186/1860-5397-4-5

• adding potassium tert-butoxide to a solution of the bromoamide in dry tetrahydrofuran at room temperature, a yield of 81% being obtained by keeping the reaction time short (25 min). To our dismay, however, the attempted thionation of 34 with Lawesson's reagent under a variety of conditions was uniformly

The enantiospecific synthesis of (+)-monomorine I using a 5-endo- trig cyclisation strategy

• Malcolm B. Berry,
• Donald Craig,
• Philip S. Jones and
• Gareth J. Rowlands

Beilstein J. Org. Chem. 2007, 3, No. 39, doi:10.1186/1860-5397-3-39

• -cyclisation, promoted by two equivalents of potassium tert-butoxide, furnished the 2,5-syn-pyrrolidine 22 as a single diastereoisomer. Concurrently with the synthesis of 22, the isopropyl model system, 14c, was prepared using analogous chemistry. Deprotection of 22 and 14c was readily achieved with Super

The vicinal difluoro motif: The synthesis and conformation of erythro- and threo- diastereoisomers of 1,2-difluorodiphenylethanes, 2,3-difluorosuccinic acids and their derivatives

• David O'Hagan,
• Henry S. Rzepa,
• Martin Schüler and
• Alexandra M. Z. Slawin

Beilstein J. Org. Chem. 2006, 2, No. 19, doi:10.1186/1860-5397-2-19

• obtained after a dehydrobromination reaction. The elimination of hydrogen bromide from such β-fluorobromides had been explored previously, and the reaction proceeds in a stereospecific manner to generate either E or Z fluoroalkene products [20]. Accordingly treatment of 14 with potassium tert-butoxide in a

Synthesis of 2,6-trans- disubstituted 5,6-dihydropyrans from (Z)-1,5-syn-endiols

• Eric M. Flamme and
• William R. Roush

Beilstein J. Org. Chem. 2005, 1, No. 7, doi:10.1186/1860-5397-1-7

• deprotection of the TBS ether by using 3HFEt3N afforded mesylates 11 (80 – ≥ 95% yield). Treatment of mesylate 11a with 1 equivalent of potassium tert-butoxide in tert-BuOH (0.01 M) between 40–50 °C provided ent-3a in 75% yield and 10:1 selectivity for the dihydropyran product and a diene resulting from an