The use of trialkylorganozincates and tetraalkylaluminates allows regioselective SN2 nucleophilic opening of vinylic epoxides. The reaction occurs with an anti-substitution pattern and can be applied to a wide range of substrates. We also show that the solvent and the structure of the epoxide have an influence on the substitution products ratio.
Chemoselective Cross Metathesis of Bishomoallylic Alcohols: Rapid Access to Fragment A of the Cryptophycins
作者:Mark Lautens、Matthew L. Maddess
DOI:10.1021/ol049883f
日期:2004.6.1
The racemic or enantioselective allylation of in situ formed beta,gamma-unsaturated aldehydes provides efficient access to bishomoallylic alcohols from readily available 2-vinyloxiranes. These products, when subjected to modified Grubbs cross metathesis conditions, afforded terminally homologated products in moderate to good yields with high E selectivity and without degradation of the enantiomeric excess. The compounds obtained through this two-step sequence yield fragments of an important and pharmacologically active family of cryptophycins.
Preparation of Homoallylic Homopropargylic Alcohols from 2-Vinyloxiranes
作者:Matthew L. Maddess、Mark Lautens
DOI:10.1021/ol051326l
日期:2005.8.1
beta, gamma-Unsaturated aldehydes generated in situ by treatment of 2-vinyloxiranes with a catalytic amount of Sc(OTf)3 or (BFOEt2)-O-. are effectively trapped by B-allenyl-9-BBN to afford homoallylic homopropargylic alcohols in high yield. An enantioselective version has been demonstrated, and a convenient synthesis of 9-allenyl-9-BBN is described.