Asymmetric Aldol Reaction of Allenoates: Regulation for the Selective Formation of Isomeric Allenyl or Alkynyl Aldol Adduct

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>Pr₂NEt, followed by addition of BF₃·OEt₂ 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

Enantioselective Synthesis of a Furan Lignan (+)-Sylvone

A synthesis of natural tetrahydrofuran lignan (+)-sylvone is achieved starting from methyl allenoate in 5 steps. The synthesis begins from an enantioselective aldol reaction of methyl allenoate with 3,4-dimethoxybenzaldehyde to afford α-addition aldol adduct. Key steps for the synthesis of sylvone include an oxacyclization of the α-hydroxy allenyl adduct followed by a Michael addition of a 1,3-dithiane derivative to establish a sylvone skeleton with suitable stereoselections