Enantioselective Synthesis of 2-Methyl-1,2-syn- and 2-Methyl-1,2-anti-3-butenediols via Allene Hydroboration−Aldehyde Allylboration Reaction Sequences
摘要:
The hydroboration of allene 7 with ((d)lpc)(z)BH at 0 degrees C provides the kinetic allylborane 12Z with >20:1 selectivity. However, when the hydroboration is performed at 85 degrees C, the kinetically formed allylborane isomerizes to give the thermodynamic allylborane 12E with >= 12:1 selectivity. Subsequent treatment of 12Z or 12E with aldehydes at -78 degrees C, followed by oxidative workup, provides the 2-methyl-1,2-diols 8 and 9 in good yield and with 80-92% e.e.
Catalytic Enantioselective and Catalyst-Controlled Diastereofacial-Selective Additions of Allyl- and Crotylboronates to Aldehydes Using Chiral Brønsted Acids
作者:Vivek Rauniyar、Dennis G. Hall
DOI:10.1002/anie.200504432
日期:2006.4.3
Enantioselective Synthesis of 2-Methyl-1,2-<i>syn</i>- and 2-Methyl-1,2-<i>anti</i>-3-butenediols via Allene Hydroboration−Aldehyde Allylboration Reaction Sequences
作者:Ming Chen、Masaki Handa、William R. Roush
DOI:10.1021/ja904599h
日期:2009.10.21
The hydroboration of allene 7 with ((d)lpc)(z)BH at 0 degrees C provides the kinetic allylborane 12Z with >20:1 selectivity. However, when the hydroboration is performed at 85 degrees C, the kinetically formed allylborane isomerizes to give the thermodynamic allylborane 12E with >= 12:1 selectivity. Subsequent treatment of 12Z or 12E with aldehydes at -78 degrees C, followed by oxidative workup, provides the 2-methyl-1,2-diols 8 and 9 in good yield and with 80-92% e.e.
Copper(I)-Catalyzed Stereodivergent Propargylation of <i>N</i>-Acetyl Mannosamine for Protecting Group Minimal Synthesis of C3-Substituted Sialic Acids
Copper(I)-catalyzed stereodivergent nucleophilic propargylation at the anomeric carbon of unprotected N-acetyl mannosamine was developed using 3-substituted allenylboronates as a nucleophile. The homopropargylic alcohol products contained two contiguous stereocenters, and two stereoisomers out of the four possible isomers were selectively obtained in a catalyst-controlled manner by applying either