Ap. Marchand et Inn. Namboothiri, Reactions of cage-annulated 2-methyl-5-(trifluoromethanesulfonyloxy)furanswith lithium diisopropylamide. Evidence for nucleophilic reactivity of LDA, HETEROCYCLE, 52(1), 2000, pp. 451-457
Reaction of 3-trifluoromethanesulfonyloxy-5-methyl-4-oxahexacyclo[5.4.1.0(2
,6).0(3,10).0(5,9).0(8,11)]dodecane (6a) with lithium diisopropylamide (LDA
, 6 equivalents) in dry THF affords 11-methylenepentacyclo[5.4.0.0(2,6).0(3
,10).0(5,9)]undecan-8-one (3a) in low yield (11%). This reaction is shown t
o proceed via formation of an intermediate cage-annulated hemiaminal (7a),
which in turn may have resulted via a highly unusual nucleophilic attack by
(i-Pr)(2)N:(-) upon exo-11-diisopropylamino-endo-11-methylpentacyclo[5.4.0
.0(2,6).0(3,10).0(5,9)]undecan-8-one (8a). The corresponding reaction of 3-
trifluoromethanesulfonyloxy-5,9,10-trimethyl-4-oxahexacyclo[5.4.1.0(2,6).0(
3,10).0(5,9).0(8,11)]dodecane (6b) with LDA (6 equivalents) in dry THF prod
uced 1,7-dimethyl-11-methylenepentacyclo[5.4.0.0(2,6).0(3,10).0(5,9)]undeca
n-8-one (3b) in 10% isolated yield.