INTRAMOLECULAR 1,6-HYDRIDE TRANSFER IN ACYCLIC 1,6-DIOLS - A MECHANISTIC STUDY

The reaction of acyclic 1,6-diol 11a with 85% phosphoric acid at tolue ne reflux yields ketone 13a through an intramolecular 1,6-hydride tran sfer. This fact is proven by using a deuterated 1,6-diol (19), in whic h the corresponding 1,6-deuteride transfer occurs. A mechanistic propo sal through a protonated oxepane (II) is formulated, which implies an actual 1,3-hydride transfer; this mechanism differs from the reported one in the literature for cyclic 1,6-diols, in which a real 1,6-hydrid e transfer takes place due to a proximity effect.