Silylstannation-Cyclization of 1,6-Enynes using Palladium(0) and Palladium(II) Catalysis

Abstract

1,6-enynes can be cyclized to 5-membered ring products bearing (tributylstannyl)methyl and exo-methylenylsilane moieties. The reaction is accomplished using either a Pd(0)/Cy₂P(o-biphenyl) complex or a cationic N-heterocyclic carbene-based Pd(II) system. The former system was found to be optimal for carbocycle formation (X = CR₂) while the latter optimal for pyrrolidine formation (X = NR). The bimetallic products could also be transformed to [3.1.0] systems through bromodestannylation or by reaction with benzaldehyde dimethyl acetal in the presence of TMSOTf.

Key words

silylstannation - palladium - catalysis - silicon - tin - carbene complexes - vinylcyclopropane

References

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14

It was found that Pd(t-BuNC)₂Cl₂ catalyzed the addition of hexabutylditin to RCH₂C≡CH to give (Z)-1,2-bis(stannyl)alkenes in 50-67% yield (5 mol% catalyst, 0.1 M THF, r.t., 24 h, e.g. R = NHBoc, 67%, R = OMe, 62%) (Figure).

Figure

22

Mori et al. have proposed a similar pathway for silylstannation-cyclization using Pd(0) catalysts, see ref. [9]