Synthesis of the spiroacetal fragment of broussonetine H

(2S,6S)-2-(3-Bromopropyl)-1,7-dioxaspiro[5.5]undecane was prepared by the addition of the acetylide derived from (4S)-4-benzyloxy-7-tert-butyldiphenylsilyloxyhep-1-yne to δ-valerolactone followed by treatment with hydrogen and palladium on charcoal which effected hydrogenation of the alkyne, hydrogenolysis of the benzyl ether and subsequent spiroacetal formation. The (4S)-stereochemistry in acetylene was established by addition of trimethylsilylacetylene to (2S)-epoxide , which in turn is derived from l-glutamic acid .