Enantioselective Allylation of <i>β</i><i>,</i><i>γ</i>-Unsaturated Aldehydes Generated via Lewis Acid Induced Rearrangement of 2-Vinyloxiranes
作者:Mark Lautens、Matthew L. Maddess、Effiette L. O. Sauer、Stéphane G. Ouellet
DOI:10.1021/ol016946a
日期:2002.1.1
[reaction: see text] 2-Vinyloxiranes have been found to be excellent surrogates to beta,gamma-unsaturated aldehydes. These valuable electrophiles, generated in situ by treatment of a 2-vinyloxirane with a catalytic amount of Sc(OTf)(3), are effectively trapped by the chiral allylating agents based on alpha-pinene, affording bishomoallylic alcohols in high yield and excellent selectivity.
β,γ‐Unsaturatedaldehydes with all‐carbon quaternary or tertiary α‐centers were rapidly assembled from ketones through a unique synthetic operation consisting of 1) C1 homologation, 2) Lewis acid mediated epoxide–aldehyde isomerization, and 3) electrophilic trapping. The synthetic equivalence of a vinyl oxirane and a β,γ‐unsaturatedaldehyde is the key concept of this previously undisclosed tactic
Zeolite (H-ZSM 5) catalysed regio and stereoselective reduction of 2,3-epoxy alcohols to 1,2-diols and vinylic epoxides to homoallylic alcohols with sodium cyanoborohydride
作者:Anuradha Gupta、Yashwant D. Vankar
DOI:10.1016/s0040-4039(98)02610-0
日期:1999.2
positions) undergo reduction with zeolite H-ZSM 5/NaCNBH3 combination of reagent system in refluxing dichloroethane to give 1,2-diols and homoallylic alcohols in moderate to good yields. Under these conditions acid sensitive groups such as an acetal and a THP ether are not affected which indicates the mildness of the reaction conditions.
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.