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Pure Appl. Chem., 2013, Vol. 85, No. 6, pp. 1149-1160

Published online 2013-03-18

Conjugate addition approach for natural product synthesis inspired by gibberellin and solanoeclepin A targets

Minoru Isobe

Department of Chemistry, National Tsing Hua University 101, Section 2, Kuang Fu Road, Hsinchu 30013, Taiwan

Abstract: Trimethylzincate is known to react through conjugate addition to α,β-unsaturated ketones, but adds much faster to α,β-unsaturated esters at low temperatures. Since the intermediate zinc enolate behaves differently from that of dimethylcuprate, it offers scope for application in a partial synthesis of gibberellin A3. A second example involving vinylsulfones having an oxygen atom on the γ-carbon strongly directs incoming nucleophiles in conjugate addition mode. Heteroatom-directed conjugate addition (HADCA) provides very reactive carbanion intermediates leading to cyclobutane ring formation, necessary for synthesis of solanoeclepin A. An alternative reaction for the four-membered carbocyclic ring closure was explored to make a bond formation between the propargylic cation of Nicholas type and allyltrimethylsilane nucleophile of Hosomi–Sakurai type. This method allowed a formation of tricyclo[,6]decene framework.