 Transfer can be facilitated under conditions of high temperature or pressure.If two equivalents of aldehyde are used, addition of the tetrahedral intermediate to a second molecule of aldehyde leads either to cyclic phosphoranes 1 or linear alkyl transfer products 2.More practical is the use of silylated phosphorus sources, which undergo intramolecular silyl group transfer in a frontside fashion, providing α-siloxy phosphorus compounds 3.