Making use of the high propensity of 2-cyano-2-cycloalkenones to undergo conjugate addition with various carbanions and the high reactivity of the ensuing α -cyano ketone system, a number of new annulation processes have been developed recently in our laboratories. As shown in Eq. 1 (n=1) with a specific example, one such process involves the addition of 3-butenylmagnesium bromide, followed by a palladium (Ⅱ) acetate mediated oxidative cyclization, to facilitate methylenecyclopentane ring formation. This annulation process could be readily extended to effect methylenecyclohexane ring formation (Eq. 1, n=2), using 4-pentenylmagnesinm bromide as the initial reagent, and to install the carbomethoxy-substituted methylenecyclopentane and methylenecyclohexane rings, using the carbanions derived from methyl 4-pentenoate and methyl 5-hexenoate, respectively (Eq. 2). In another annulation process, the addition of the enolate of methyl 5-chloropentanoate is involved initially, and the ring formation is readily effected by an intramolecular alkylation process. A specific example is given in Eq. 3.
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