diastereoselectivity of the initial tandemreactions was estimated to be 94:6 from the 31P NMR of a mixture of the diastereomeric ketal derivatives 6a and 6'a which were obtained by the reaction of 5a with (2R,3R)-2,3-butanediol, and the absolute configuration of the major isomer was determined by the single-crystal X-ray analysis. Similar reactions using some 8-phenylmenthyl alkenoates were attempted. As a result
Diastereoselectivity in the preparation of β-silylesters from αβ-unsaturated esters and amides attached to chiral auxiliaries
作者:Ian Fleming、Nicholas D. Kindon
DOI:10.1039/c39870001177
日期:——
phenyldimethylsilyl-cuprate reagent to cinnamate and crotonate esters and amides of various known chiral auxilaries is diastereoselective, making available β-silylesters of high enantiomeric excess; the sense of the diastereoselectivity is anomalously different from established precedent in the case of silyl-cuprate addition to the cinnamate ester (1, R = Ph, R*=d).
Highly Diastereoselective Synthesis of Vinylcyclopropane Derivatives with (−)-8-Phenylmenthol as Chiral Auxiliary
作者:Song Ye、Yong Tang、Li-Xin Dai
DOI:10.1021/jo010121x
日期:2001.8.1
telluronium allylide 4, generated in situ from the corresponding telluronium salt in the presence of LiTMP, reacted with (-)-8-phenylmenthyl alpha,beta-unsaturated esters to afford trans-2-silylvinyl-trans-3-substituted cyclopropyl esters with high diastereoselectivity in high yields. The absolute configuration was determined by chemical transformation. A mechanistic rationale is proposed.
The reaction of tert-butylalkynyl chromium Fischercarbenecomplex 1 with nitrones 2 affords β-enamino-ketoaldehydes 4 by the light-promoted rearrangement of the corresponding [3+2] cycloadduct carbenecomplexes3. On the other hand, [3+2] cycloaddition of chiral nonracemic Fischeralkenylcarbenecomplexes 19 with nitrilimines 10 yields enantiomerically pure Δ2-pyrazolines with high regio- and diastereoselectivity
Diamination of Olefins: Synthesis, Structures and Reactivity of Osmaimidazolidines
作者:Kilian Muñiz、Atsushi Iesato、Martin Nieger
DOI:10.1002/chem.200305011
日期:2003.11.21
obtained from olefin difunctionalisation were characterised by X-ray analysis for the first time. Kinetic studies on the reaction profile have also been carried out. An asymmetric version of this reaction is based on chiral non-racemic auxiliaries and leads to diastereomerically enriched osmaimidazolidines with up to 90 % de. This sequence represents the first asymmetric diamination of olefins. Attempts