Allylation Using Allylborates

Article abstract of DOI:10.1016/S0040-4020(01)80802-4

A study has been carried out on the scope of allylation of a range of acetals activated by trimethylsilyl trifluoromethanesulfonate (TMSOTf) using a number of organoborates.Intermolecular allylation of acyclic acetals proceeds smoothly and in high yield using lithium n-butyltriallylborate or lithium methyltriallylborate in THF at -78 deg C while 1,3-dioxanes and dioxolanes give rise to some reduction products.Intramolecular allylation may be carried out via anchoring the triallylborane using an alkoxide anion.Mechanistic studies indicate that allyl transfer is from boron and not silicon, while stereoselectivity studies on the crotylation of acyclic acetals as well as the allylation of chiral acetals derived from (2R,4R)-pentanediol indicate moderate levels of diastereoselection.