Studies towards the total syntheses of (+)-phomactins A, D and G

Studies towards the total synthesis of (+)-Phomactin A (1), D (6), and G (9), fungal metabolites with unique molecular architecture and pronounced biological activity, are described. These studies resulted in the synthesis of advanced intermediates 354 and 356, which contain all of the carbon atoms of 1, 6 and 9. A Horner-Wadsworth Emmons olefination of aldehyde 186 and beta-keto ester 289 was utilized to construct enone 311. A novel Stryker conjugate reduction/aldol cyclization sequence provided alcohol 312, constituting the B ring of 1, 6 and 9. A subsequent elimination of the alcohol in 312 provided a divergence point towards 6 and 9. Attempts to close the 12-membered macrocycle of 6 and 9 from 303 and 316/317 via ring closing metathesis solely provided intermolecular metathesis products 318 and 319 .;A second generation approach to close the 12-membered macrocycle exploited the use of a relay ring closing metathesis. This method exploited the use of a relaying tether to orchestrate catalyst movement to close the macrocycle of 354 and 356.