Sulfone-mediated syntheses of crocetin derivatives: regioselectivity of highly functionalized building blocks

Bromoacetate Olefination Protocol for Norbixin and Julia-Kocienski Olefination for Its Ester Syntheses

A new olefination protocol utilizing ethyl bromoacetate was highlighted, in which magnesium enolate of the ester coupled with C₂₀ dialdehyde 6, and double eliminations of the protected hydroxyl groups and bromine atoms of the coupling bromohydrin product, efficiently produced norbixin 1 after concomitant hydrolysis of the ester. A new (C₇ + C₁₀ + C₇) disconnection approach was demonstrated for the synthesis of norbixin ethyl ester 2 by the Julia-Kocienski olefination of novel C₇ benzothiazolyl-sulfone 11 and C₁₀ 2,7-dimethyl-2,4,6-octatrienedial (12).