Lipase-catalyzed kinetic resolution of .gamma.-hydroxy phenyl sulfones
摘要:
Lipase PS (from Pseudomonas cepacia) catalyzed the enantioselective transesterification of racemic gamma-hydroxy-alpha,beta-unsaturated phenyl sulfones 1 and their alpha,beta-saturated derivatives 3 with vinyl acetate in an organic solvent (usually (i)Pr2O). Remarkably, in substrates 1 with (E)-stereochemistry, the enantioselectivity of the process was little influenced by the nature of the R chain. Hence, very high enantiomeric ratios (E greater-than-or-equal-to 45) were observed in substrates 1 bearing short (R = Me or Et), long (R = n-Cr6H13 or n-C10H21), bulky (R = (i)Pr), or functionalized R chains. The (R)-enantiomer was the fast-reacting enantiomer in all cases. Concerning the reactivity, the rate of the reaction decreased significantly with an increase in size or length of the R chain (reaction time for 50% conversion from 3.5 to 162 h). Less satisfactory enantioselectivities (E = 5-48) were obtained when the saturated substrates 3 were used instead of the corresponding alpha,beta-unsaturated alcohols 1.
Stereoselective Synthesis of Polyhydroxylated Indolizidines from γ-Hydroxy α,β-Unsaturated Sulfones
摘要:
The polyhydroxylated indolizidines castanospermine and swainsonine as well as some of their stereoisomers are powerful glycosidase inhibitors. An efficient and stereochemically flexible synthesis of racemic 1,7,8-trihydroxylated and 1,6,7,8-tetrahydroxylated indolizidines (castanospermine stereoisomers) from readily available N-substituted gamma-oxygenated alpha,beta-unsaturated sulfones 3 and 4 has been developed. The construction of the bicyclic skeleton of 1-hydroxyindolizidine has been accomplished by intramolecular conjugate addition of the nitrogen moiety of 3 and 4 to the alpha,beta-unsaturated sulfone unit to give the pyrrolidine intermediates 5 and 6, followed by formation of the C(7)-C(8) bond by intramolecular acylation (or alkylation) of the alpha-sulfonyl carbanion. The stereoselectivity of the pyrrolidine synthesis was highly dependent on the bulkiness of the gamma-oxygenated function; thus, the free alcohols gave predominantly cis-pyrrolidines while the OTIPS derivatives led to the trans isomers. After straightforward functional group transformations, the removal of the sulfonyl group at C(8) either by Julia reaction or by basic elimination (depending on the substrate used) afforded the key C(7)C(8) unsaturated indolizidines 10, 22, 30, and 31, whose stereoselective dihydroxylations with OsO4 gave a variety of cis C(1)C(8a) and-trans C(1)C(8a) trihydroxylated and tetrahydroxylated indolizidines, among which (+/-)-1,7-di-epi-castanospermine and (+/-)-1,8-di-epi-castanospermine have been reported for the first time.
evaluation of the chemical and stereochemical scope of the process in comparison with the Pauson-Khand cyclization of non-sulfonylated enynes, its application to the stereoselectivepreparation of optically pure C6-substituted bicyclo[3.3.0]oct-1-en-3-ones, and the interpretation of the stereochemical outcome are also discussed.
Stereoselective synthesis of hydroxypyrrolidines and hydroxypiperidines by cyclization of γ-oxygenated-α,β-unsaturated sulfones
作者:Juan Carlos Carretero、Ramón Gómez Arrayás、Isabel Storch de Gracia
DOI:10.1016/0040-4039(96)00551-5
日期:1996.5
cis and trans 2,3-disubstituted pyrrolidines and piperidines have been prepared stereoselectively by intramolecular conjugate addition of N-substituted γ-oxygenated-α,β-unsaturated phenyl sulfones. The best cis-selectivities were obtained from the alcohols and the best trans-selectivities from the OTIPS derivatives.
An efficient and stereoselective synthesis of enantiopure 1,2,7-trihydroxylated pyrrolizidines
作者:Javier de Vicente、Ramón Gómez Arrayás、Juan C. Carretero
DOI:10.1016/s0040-4039(99)01265-4
日期:1999.8
An efficient approach to the stereoselective synthesis of enantiopure 1,2,7-trihydroxylated pyrrolizidines from the readily available optically pure γ-hydroxy-α,β-unsaturated sulfone 2a is described.
γ-Oxygenated-α,β-unsaturated sulfones in radical cyclizations and cascade processes
作者:Javier Adrio、Juan C Carretero
DOI:10.1016/s0040-4020(97)10368-4
日期:1998.2
(substrates 1–4) have been prepared. Both 5-hexenyl and 6-heptenyl radicals, generated by reaction of substrates 1–4 with Bu3SnH/AIBN, underwent an efficient cyclization via intramolecular addition to the vinyl sulfone moiety. By introduction of a double bond joined to the oxygen at γ-position, a cascade process based on two sequential radical cyclizations took place, affording highly substituted 2-oxa[3