A Further Synthetic Approach to the Adamantane Isomer 2, 5‐Trimethylenenorbornane (Tricyclo [5.3.0.0^3,9]decane, 4‐Homotwistbrendane)

Abstract

SummaryA further synthetic approach to 2,5-trimethylenenorbornane (1; tricyclo- [5.3.0.03,9]decane, 4-homotwistbrendane), a member of the 'adamantaneland', is described starting from methyl 5-0x0-2endo-norbornanecarboxylate (5). The required C2-chain was introduced by a Wittig-Horner reaction and the ring closure of the trimethylene bridge achieved by an acyloin condensation.In the course of our studies on isomeric tricyclic hydrocarbons of the 'adamantaneland' '), we recently described a first synthesis of the title isomer, 2,5-trimethylenenorbornane (1)'). Solvolysis of the p-toluenesulfonate 2 of protoadamant-4-en-loendo-01 yielded among others the allylic alcohols 3 and 4 with the desired C-skeleton [2]. Subsequent conversions of the iatters led to 1.In view of further investigations on the adamantane rearrangement of 1, especially with specifically labelled analogues, we report a second synthetic approach to 1 and derivatives thereof, starting from the properly 2,5-difunctionalized norbornane 5. As the only evaluated synthesis of 5 (31 is an unspecific one, we decided to prepare 5 from the known ester 6 [4] by the following route: epoxidation and lactonization of 6 with trifluoroperacetic acid [S] gave the known [6] hydroxy lactone 7 (94%), which was oxidized to the keto lactone 8 (80%) with