Vicarious nucleophilic substitution of hydrogen (VNS) in 1,4-naphthoquinone derivatives - competition between VNS and vinylic nucleophilic substitution (SNV)

Carbanions of dimethyl chloromalonate, ethyl 2-chloroacetoacetate and dimet hyl malonate react with naphthoquinone derivatives mainly via vicarious nuc leophilic substitution or oxidative nucleophilic substitution of hydrogen p rocesses. These reactions in 2-halo substituted naphthoquinones are general ly faster processes than vinylic nucleophilic substitution of halogen (SNV) . Introduction of one Cl substituent into position 2- of 1,4-naphthoquinone increases substantially its electrophilic activity resulting in much faste r addition of the carbanion in the position occupied by hydrogen. On the ot her hand addition of the carbanions to 2,3-dichloro-1,4-naphthoquinone proc eeds slower than to 1,4-naphthoquinone. (C) 2001 Published by Elsevier Scie nce Ltd.