Homoallylic amines by reductive inter- and intramolecular coupling of allenes and nitriles

• Peter Wipf and
• Marija D. Manojlovic

Beilstein J. Org. Chem. 2011, 7, 824–830, doi:10.3762/bjoc.7.94

• equatorial position, placing the electronegative carbamate substituent and the C–O bond in the tetrahydropyran ring into a gauche orientation (Figure 1). We propose a chelated transition state for the formation of 19, 21, and 23 (Scheme 3). After the initial hydrozirconation and transmetallation with

The arene–alkene photocycloaddition

• Ursula Streit and
• Christian G. Bochet

Beilstein J. Org. Chem. 2011, 7, 525–542, doi:10.3762/bjoc.7.61

• reaction involves the formation of a new aryl C–C bond and the loss of the aryl C–O bond, and is therefore clearly a rearrangement product. Furthermore, Sakamoto showed that this reaction was not limited to benzophenones, but also occurred with acetophenones, albeit in slightly lower yields. For this

An efficient and practical entry to 2-amido-dienes and 3-amido-trienes from allenamides through stereoselective 1,3-hydrogen shifts

• Ryuji Hayashi,
• John B. Feltenberger,
• Andrew G. Lohse,
• Mary C. Walton and
• Richard P. Hsung

Beilstein J. Org. Chem. 2011, 7, 410–420, doi:10.3762/bjoc.7.53

• -dienes see [51][52]). Problems with the two primary approaches to access amido-dienes [47] are that acid-mediated condensations suffer from functional group tolerances, and metal-mediated coupling methods (for reviews on Cu-mediated C–N and C–O bond formations see [53][54][55], for some examples see [56

C–C (alkynylation) vs C–O (ether) bond formation under Pd/C–Cu catalysis: synthesis and pharmacological evaluation of 4-alkynylthieno[2,3-d]pyrimidines

• Dhilli Rao Gorja,
• K. Shiva Kumar,
• K. Mukkanti and
• Manojit Pal

Beilstein J. Org. Chem. 2011, 7, 338–345, doi:10.3762/bjoc.7.44

• /C–CuI–PPh3 catalytic system facilitated C–C bond formation between 4-chlorothieno[2,3-d]pyrimidines and terminal alkynes in methanol with high selectivity without generating any significant side products arising from C–O bond formation between the chloro compounds and methanol. A variety of novel 4

• the expected product via a C–C bond forming reaction (Scheme 3, path a) and no side product as a result of C–O bond formation [11] due to participation of MeOH (Scheme 3, path b) was detected in the reaction mixture. The use of MeOH as a nucleophile in Pd-catalyzed reactions has been well documented

• -alkynylthieno[2,3-d]pyrimidine (3). A C–O bond forming reaction between 1 and MeOH (Scheme 2, path b) was not observed perhaps due to the higher reactivity of copper acetylide over MeOH (even although present in excess) towards E. We have shown that an alkynyl moiety can be introduced efficiently at the C-4

Novel multi-responsive P2VP-block-PNIPAAm block copolymers via nitroxide-mediated radical polymerization

• Cathrin Corten,
• Katja Kretschmer and
• Dirk Kuckling

Beilstein J. Org. Chem. 2010, 6, 756–765, doi:10.3762/bjoc.6.89

• the nitroxide-group, which takes place during the MALDI measurement. Disregarding the mechanism, Scheme 2 describes the possible reactions. Since this process is accompanied by other degradation processes such as ß-abstraction [41] and by the instability of the C–O bond, it was not possible to detect

Novel tetracyclic structures from the synthesis of thiolactone-isatin hybrids

• Renate Hazel Hans,
• Hong Su and
• Kelly Chibale

Beilstein J. Org. Chem. 2010, 6, No. 78, doi:10.3762/bjoc.6.78

• containing a bridged amide bond. Essentially, the amide functionality adopts a planar conformation in normal amides with stability being conferred by the delocalization of the nitrogen lone pair into the C=O bond [25]. The amides in bicyclic bridgehead lactams are distorted from planarity and this severely

• carbon and nitrogen pyramidality (χC and χN) and the N-C(=O) and C=O bond lengths (Table 3) all indicate that the bridge amide bond is essentially relaxed. In summary we have described the straightforward synthesis of novel compounds 3 and 4. The latter bears quaternary stereogenic centers and a

The C–F bond as a conformational tool in organic and biological chemistry

• Luke Hunter

Beilstein J. Org. Chem. 2010, 6, No. 38, doi:10.3762/bjoc.6.38

• organofluorine molecule and these can be substantially stronger. For example, in α-fluoroamides (e.g. 3, Figure 1a) there is a strong preference for the C–F bond to align antiparallel to the C=O bond, a conformation in which the C–F dipole opposes the amide dipole. An analogous effect exists with other α

• case of β-peptide 66, the fluorine atom aligns antiparallel to the adjacent C=O bond and gauche to the adjacent amide nitrogen, and this reinforces the helical conformation of the β-peptide. In contrast, the helical conformation of β-peptide 67 cannot accommodate these favourable alignments, so in this

• conformational influence of the C–F bond, which is forced into a high-energy orientation orthogonal to the adjacent C=O bond. Nevertheless, taken together, the results with β-peptides (Figure 18) show that a single C–F bond can have a dramatic impact on peptide conformation. Future directions Recent results

Diastereoselective functionalisation of benzo-annulated bicyclic sultams: Application for the synthesis of cis-2,4-diarylpyrrolidines

• Susan Kelleher,
• Pierre-Yves Quesne and
• Paul Evans

Beilstein J. Org. Chem. 2009, 5, No. 69, doi:10.3762/bjoc.5.69

• would be anti-Bredt) and in addition the lone pair is perpendicular to the p-orbital resulting from C–O bond cleavage. Furthermore, it also appears that the aromatic ring, based on the fold of the molecule, represents a steric barrier blocking the approach to the C–O σ* orbital. Since the bicyclic

Pd/C-mediated synthesis of α-pyrone fused with a five-membered nitrogen heteroaryl ring: A new route to pyrano[4,3-c]pyrazol-4(1H)-ones

• Dhilli Rao Gorja,
• Venkateswara Rao Batchu,
• Ashok Ettam and
• Manojit Pal

Beilstein J. Org. Chem. 2009, 5, No. 64, doi:10.3762/bjoc.5.64

• pyrano[4,3-c]pyrazol-4(1H)-ones under Pd/C-Cu catalysis, preparation of which would be difficult via other methods. The reaction proceeds via tandem C-C and C-O bond formation between the 5-iodopyrazole-4-carboxylic acid and a terminal alkyne in the same pot. Being an integral part of many drugs or

Iridium-catalyzed asymmetric ring-opening reactions of oxabicyclic alkenes with secondary amine nucleophiles

• Dingqiao Yang,
• Ping Hu,
• Yuhua Long,
• Yujuan Wu,
• Heping Zeng,
• Hui Wang and
• Xiongjun Zuo

Beilstein J. Org. Chem. 2009, 5, No. 53, doi:10.3762/bjoc.5.53

• 1a are then reversibly coordinated to the iridium center of the catalyst to give the intermediate C. Oxidative insertion of C in to the C–O bond forms D. Then, attack of the secondary amine nucleophile along with configurational inversion is proposed to occur in an SN2′ displacement of the iridium

Synthesis of imidazol- 1-yl-acetic acid hydrochloride: A key intermediate for zoledronic acid

• Santosh Kumar Singh,
• Narendra Manne,
• Purna Chandra Ray and
• Manojit Pal

Beilstein J. Org. Chem. 2008, 4, No. 42, doi:10.3762/bjoc.4.42

• facilitates the cleavage of the C–O bond attached to the tert-butyl group. The HCl generated during this conversion is trapped by the imidazole (to form a salt). Treatment with i-PrOH produces the desired acid 6. Having prepared the key intermediate 6, it was converted to zoledronic acid (7) in 57% yield by

Synthesis of spiropyrans: H-abstractions in 3-cycloalkenyloxybenzopyrans

• Satish C. Gupta,
• Mandeep Thakur,
• Somesh Sharma,
• Urmila Berar,
• Surinder Berar and
• Ramesh C. Kamboj

Beilstein J. Org. Chem. 2007, 3, No. 14, doi:10.1186/1860-5397-3-14

• of 2 (R = CH3) could be that the presence of -CH3 group on dihydrofuryl moiety in the photoproduct 5 (R = CH3) makes the C-O bond easier to cleave. Thus as soon as 5 (R = CH3) is formed, it rearranges to 7 (R = CH3) or in other words the conversion of 5 (R = CH3) into 7 (R = CH3) is much faster than

Photosonochemical catalytic ring opening of α-epoxyketones

• Hamid R. Memarian and
• Ali Saffar-Teluri

Beilstein J. Org. Chem. 2007, 3, No. 2, doi:10.1186/1860-5397-3-2

• only in thermal but also in photochemical transformations. Single electron transfer (SET) induced ring opening reactions of epoxides and α-epoxyketones have demonstrated C-C and C-O bond cleavages through photo-induced electron transfer by various electron donors such as triethylamine (TEA), [21

Effect of transannular interaction on the redox- potentials in a series of bicyclic quinones

• Grigoriy Sereda,
• Jesse Van Heukelom,
• Miles Koppang,
• Sudha Ramreddy and
• Nicole Collins

Beilstein J. Org. Chem. 2006, 2, No. 26, doi:10.1186/1860-5397-2-26

• methoxy-substituents. They explained this difference by the parallel alignment of the C-O-bond with the π-system of the benzene ring, which amplifies the inductive effect of the methoxy-group. In other words, quinone 2 assumes the conformation B. As we move from the conformation A to conformation B

Do α-acyloxy and α-alkoxycarbonyloxy radicals fragment to form acyl and alkoxycarbonyl radicals?

• Dennis P. Curran and
• Tiffany R. Turner

Beilstein J. Org. Chem. 2006, 2, No. 10, doi:10.1186/1860-5397-2-10

• for fragmentation is even smaller. Even if the β-fragmentation is occurring by a radical pathway, it is so slow as to have limited synthetic value in radical chain sequences. The sluggishness of these β-fragmentation reactions is surprising, especially give that they produce a strong C=O bond and 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

• allylic alcohol to be displaced in this intramolecular substitution process, the allylic C-O bond substantially deviates from coplanarity with the adjacent π-system. Therefore, the difference in relative rates of displacement of the two activated hydroxyl groups is much less than originally anticipated