An approach to the synthesis of the C(17)-C(27) fragment of bryostatins

The organolithium reagent generated from the vinyl iodide 8 reacts with aldehyde 13 to give a mixture of the anti- and syn-silyloxy alcohols 14 and 15 together with the regioisomeric syn-silyloxy alcohol 16, ratio 14:15: 16 = 4: 1 : 1. The major anti-alcohol 14 was taken through to the methoxyacetal 27 so confirming this strategy for the stereoselective synthesis of the C(17)-C(23) fragment of bryostatins. The diol 30, which has configurations at each of its three chiral centres corresponding to the C(23)-C(27) fragment of bryostatins, was prepared in two steps from the aldehyde 28 and converted into the vinylstannane 45. (C) 1998 Elsevier Science Ltd. All rights reserved.