Synthetic studies toward bryostatin 1: preparation of a C1-C16 fragment by pyran annulation

An expeditious assembly of a C1-C16 subunit of bryostatin 1 is described. A pyran annulation reaction was utilized to form the B-ring by reaction of a hydroxy-allylsilane with a fully elaborated A-ring subunit. This annulation process proceeded with complete diastereoselectivity and in excellent isolated yield despite the presence of potentially sensitive functionality in the A-ring segment.