4-(Trialkylsilyl)oxybut-2-ynals as dienophiles in the Diels–Alder synthesis of α-(hydroxymethyl)benzaldehydes

The α-(hydroxymethyl)benzaldehyde derivative 2 has been synthesized by heating ynal 3 with diene 5, which produced the α-(silyloxymethyl)benzaldehyde 6 by a Diels–Alder/retro-Diels–Alder process, followed by methylation, thioacetalization, and removal of the silyl protecting group. Decarbonylation of α-(silyloxymethyl)benzaldehydes 6 and 10 takes place readily in the presence of zinc(II) chloride or para-toluenesulfonic acid.