Asymmetric Aldol Reaction of Allenoates: Regulation
for the Selective Formation of Isomeric Allenyl or Alkynyl Aldol Adduct
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Abstract
A highly
stereoselective synthesis of 3-butynyl-<i>threo</i>-aldol
adducts is achieved from the reaction of allyl allenoate with a chiral
bromoborane in the presence of <i>i</i>Pr<sub>2</sub>NEt,
followed by addition of BF<sub>3</sub>路OEt<sub>2</sub> as an
additive to scavenge excess base and then aldehydes, whereas isomeric
allenyl aldol adducts are formed in the absence of a Lewis acid additive
from methyl allenoate