Vinyl epoxides formation, allylic derivatives

The palladium-catalyzed [3 + 2] cycloaddition of vinylic oxirane 20a [42] and aziridine 20b [39] with the activated olefin 4a for the formation of five membered cyclic ether 21a and pyrrolidine derivative 21b has also been reported in our laboratories. The mechanistic issue is very much similar to that discussed in Scheme 9. Pd(0) catalyst added oxidatively to 20 to produce the 7r-allylpalladium complex 22. The Michael addition of a hetero nucleophile in 22 to the activated olefin 4a gives 23 which undergoes intramolecular nucleophilic attack on the inner 7r-allylic carbon atom to give the cy-clized products 21 and Pd(0) species is generated (Scheme 10). Similarly, the palladium-catalyzed [3 + 2] cycloaddition of vinylic oxirane 20a with the N-losylimincs 24 is also known (Scheme 11) [43]. Intermolecular cycloaddition of vinyl epoxides and aziridines with the heterocumulenes such as isocyanates, carbodiimides and isothiocyanates is also known [44,45]. Alper et al. reported the regio- and enatioselective formation of the thiaolidine, oxathiolane, and dithiolane derivatives by the palladium-catalyzed cyclization reaction of 2-vinylthiirane with heterocumulenes [46]. 

The resulting derivatives were applied with success in the standard asymmetric allylic alkylation (up to 97 % ee) [134, 136] or in transformations involving either specific allylic substrates (2-cycloalkenyl derivatives, up to >99% ee) [135, 137], unsymmetrical substrates (monosubstituted allyl acetate, up to 83% ee) [140], or especial nucleophiles (nitroalkanes [141], iminoesters [138 a], or diketones [139, 140, 142]). Such ligands were also effective in the formation of quaternary chiral carbon through allylic substitution (eq. (6)) [138, 143], deracemiza-tion of vinyl epoxides (up to 99% ee) [144], or alkylation of ketone enolates [138 b], and deracemization of allylic derivatives [145]. 

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