Methanol promotes the addition of allyltrimethylstannane (1a) to isobu
tyraldehyde (2a, 30 degrees C) yielding the corresponding homoallylic
alcohol (3a), without the necessity for added catalyst. The correspond
ing reaction of aldehydes 2a-e or activated ketone 2f with tetraallylt
in (1b, 0.25 equiv) is substantially faster and proceeds in high yield
(81-98%) and with easy separation of the product from tin residues. A
liphatic ketones 2g and 2h also react, but require more forcing condit
ions, Competitive experiments involving equimolar mixtures of selected
aldehydes and ketones with 1b indicates very high aldehyde chemoselec
tivity. The reaction of 1b with aldehydes proceeds slowly at first, fo
llowed by a rapid acceleration which may be attributable to a build up
of partially soluble tin(TV) methoxide. The increased rate of carbony
l allylation by 1a and 1b in methanol, relative to dimethyl sulfoxide,
suggests that the primary activating influence of the solvent is via
hydrogen bonding to the carbonyl oxygen. There is no NMR spectroscopic
evidence for a significant change in the ground state structure of th
ese allylic stannanes in methanol, relative to other solvents.