Cyano-Involved Michael-Cyclization Reaction

Zhao et al. also presented the asymmetric synthesis of multifunctionalized 47f-pyran derivatives 181 with malononitrile 180 as the nucleophile. The Michael-cyclization reaction of active p,y-unsaturated a-keto esters 179 and malononitrile 

SCHEME 248 a,a-Dicyanoolefin-involved asymmetric Michael-cycUzation reaction. 

SCHEME 249 Asymmetric synthesis of 4fl-pyrans employing malononitrile as a nncleophile. 

SCHEME 2.50 Tandem Michael-cyclization process for the synthesis of ehiral 

Interestingly, when the nucleophiles were replaced by a-nitro ketones 194 under the promotion of tertiary amino thioureas, the Michael-haniketalization products would undergo further acyl transfer reaction to afford 5-nitro-2-acyloxy-pen-2-enoates 195, as described independently by Gao et al. [77a] and Lu et al. [77b] (Schane 2.52). 

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