RADICAL CASCADES IN SYNTHESIS - DIOXATRIQUINANES AND DOUBLY-ANNULATEDGLYCOSIDES BY TRIETHYLBORANE-INDUCED ATOM-TRANSFER CYCLIZATION OF 1,5-ENYNES AND 1,5-DIYNES

Tandem radical reactions listed in the title afford a convergent and f lexible pathway to functionalized, heteroannular tricyclic acetals whi ch are of relevance in natural product chemistry. The cycloisomerizati on of the 1,5-enyne was carried out under exceptionally mild condition s at -50 to -65 degrees C. For the first time, consecutive 5-exodigona l / 5-exo-digonaI cyclizations using 1,5-diyne systems have been accom plished again under full stereocontrol.