A Stereospecific Synthesis of Methyl (+)- Trans -chrysanthemate from (+)-?-Pinene

Abstract

In continuation of our studies on the synthesis of chrysanthemic acid and its analogues as potential insecticides with low mammalian toxicity we now wish to describe the stereospecific synthesis of natural (+)-(1R, 3R)-trans-chrysanthemic acid methyl ester 1 from (+)- (1R, 5R)-α-pinene 2 via Favorskii ring contraction of an appropriately substituted α-bromocyclobutanone intermediate. Barlier we had described two syntheses of 1 ^1,2 from (+)—(1S, 6R)-car-3-ene 3. The absolute configuration of 1 is now well established³ and a perusal of the absolute structures of 1, 2 ⁴ and 3 ⁵ as shown in the accompanying figures clearly indicates that the C-3 chiral centre of 1 has the same absolute configuration as C-5 of 2 and C-6 of 3.