A Convenient and Diastereoselective Route to Homoallyl Alcohols: Addition of (Z)- or (E)-Alkenyl-dimethoxyboranes to Aldehydes

Article abstract of DOI:10.1002/hlca.19820650415

(Z)-2-Butenyl-dimethoxyborane adds smoothly to propanal and benzaldehyde to afford the homoallyl alcohols (R*,R*)-1 and (R*,R*)-2.In contrast (E)-2-butenyl-dimethoxyborane leads to adducts having the (R*,S*)-configuration.Dimethoxy-(Z)-2-pentenylborane, dimethoxy-(Z)-(2-methyl-2-butenyl)borane and (2Z,4E)- or (2E,4Z)-hexadienyl-dimethoxyborane, treated with propanal, give (R*,R*)-3, (R*,R*)-4, (E),(R*,S*)-5 and (Z),(R*,R*)-5, respectively.A transition state model implying a pericyclic electron motion is in perfect agreement with the regio- and stereoselective outcome of these borane reactions.