A Claisen-type cyclisationt81 of 2 was precluded by the presence of the base-sensitive phenylsulfonyl group. Therefore the specific lithium enolate 3 was trapped with trimethylsilyl chloride to give 4 which was washed with brine to remove HMPA t-3). Treatment of crude 4 with a catalytic amount of trimethylsilyl triflate(101 smoothly effected the cyclisation. Compound 5 was obtained in 68% overall yield as a single diastereoisomer.
