REGIOSELECTIVITY AND STEREOSELECTIVITY OF ADDITIONS OF ORGANOMETALLICS TO ENDO- AND EXO-TRICYCLO[5.2.1.0(2,6)]DECA-4,8-DIEN-3-ONES

The regio- and stereoselectivity of the addition of selected organomet allics to endo- and exo-tricyclodecadienones 12, 18 and 21 are describ ed. RLi and R(2)Culi add with complete 1,2- and 1,4-regioselectivity, respectively, the additions of RMgX and RMgX/CuX are only slightly les s selective. Additions to 12 and 21 occur from the convex exo-face onl y, irrespective of the nature of both reagent and substrate. In contra st, organometallic species add from both the concave and the convex fa ce to tricyclic ester 18, with a selectivity that depends on the type of organometallic reagent. The observed stereoselectivities of the add itions are rationalized by invoking steric control by the C-8-C-9 ethy lene bridge in 12, by the C-10 methylene bridge in 21 and by both the C-8-C-9 ethylene bridge and the exo-ester function at C-2 in tricyclic ester 18.