End game strategies towards the total synthesis of vibsanin E, 3-hydroxyvibsanin E, furanovibsanin A, and 3-O-methylfuranovibsanin A

• Brett D. Schwartz,
• Craig M. Williams and
• Paul V. Bernhardt

Beilstein J. Org. Chem. 2008, 4, No. 34, doi:10.3762/bjoc.4.34

• obtained as the minor component. Furan 41 is an interesting molecule in that it contains a bridgehead double bond, presumably formed due to the ease of carbocation formation at the benzylic (tertiary) centre. Unfortunately, the bridgehead double bond contained within 41 could not be hydrated. Conversion of

Diels- Alder reactions using 4,7-dioxygenated indanones as dienophiles for regioselective construction of oxygenated 2,3-dihydrobenz[f]indenone skeleton

• Natsuno Etomi,
• Takuya Kumamoto,
• Waka Nakanishi and
• Tsutomu Ishikawa

Beilstein J. Org. Chem. 2008, 4, No. 15, doi:10.3762/bjoc.4.15

• cleavage was expected by the aid of the 4-methoxy group due to the deactivation of the 9-methoxy group by conjugation with the carbonyl at the 1 position to afford desired 4,8,9-trioxygenated compound 28 (Path C, Scheme 5). However, protonation of the carbonyl oxygen of 11 could yield a C-4a carbocation 37

Generation of pyridyl coordinated organosilicon cation pool by oxidative Si-Si bond dissociation

• Toshiki Nokami,
• Ryoji Soma,
• Yoshimasa Yamamoto,
• Toshiyuki Kamei,
• Kenichiro Itami and
• Jun-ichi Yoshida

Beilstein J. Org. Chem. 2007, 3, No. 7, doi:10.1186/1860-5397-3-7

• C-S bond dissociation. Very recently, the oxidative C-C bond dissociation has been found to be effective for generation of a pool of a carbocation having a stabilizing group as shown in Scheme 1[6]. We have been interested in generation and accumulation of cations of other elements such as silicon

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

• leads us to assume that the inductive effect of the p-methyl group and the resonance effect of the p-methoxy group on the phenyl ring directly attached to the epoxide ring increase the contribution of the intermediates 6 and 7 because of the stabilization of carbocation or carbocation-like centers. The

• more stable conformer of the intermediate 7 can be formed through interaction of oxygen lone pair of carbonyl group with carbocation center (Scheme 4, intermediate 8). This leads to the preferred nucleophilic attack of methanol to the carbon atom at the less hindered site (VII) to form the cis-isomers

• pair of carbonyl group with carbocation center. Photochemical and photosonochemical reactions of 1a-f catalyzed by 2 in methanol solution.I UV absorption λmax and molar extinction coefficients (ε)of 1a-f and NBTPT in CH2Cl2 Mulliken electric charges [52][53] of the epoxide ring atoms of 1a-f alone and

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

• as the major erythro-13 isomer must arise by replacement of the bromine of anti-14 by fluorine with an overall retention of configuration. Various examples of anchimeric assistance by phenyl groups have been reported [22] and in this case a carbocation is most reasonably generated which finds

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

• diethyl azodicarboxylate or Ph3P-CCl4 were low yielding (entries 1, 2).[22] Interestingly, small amounts of the 2,6-cis-disubstituted dihydropyran 6a were detected under these conditions, suggesting the intervention of a competitive double inversion process or a carbocation-mediated cyclization process