Modular Total Syntheses of Lamellarin G Trimethyl Ether and Lamellarin S

Modular total syntheses of the title compounds 2 and 3 are reported. The key pyrrolic building block 8 was prepared from the readily accessible pyrrole 6 via a di-iodination/mono-deiodination sequence. Suzuki-Miyaura cross-coupling of compound 8 with boronate ester 9 afforded lactone 10. Bromination of compound 10 followed by N-alkylation under Mitsunobu conditions afforded the fully substituted pyrrole 13 that engaged in a second Suzuki-Miyaura cross-coupling reaction with boronic acid 14 to give compound 15. Hydrolysis of the ester moiety within the last compound afforded acid 16 that engaged in a decarboxylative Heck cyclization process to give lamellarin G trimethyl ether (3). A related sequence of reactions starting from building block 8 and using the isopropoxy-substituted arenes 22, 25 and 27 has allowed for the completion of the first total synthesis of lamellarin S (2).