Synthesis of C-homoerysodienone and its conversion into B-homoerysodienone via a dibenz[d,f]azecine; potential precursors of the homoerythrina alkaloids

Abstract

C-Homoerysodienone (12) was synthesised by the unambiguous route (26)→(27)→(28)→(30)→(32)→(12) with a high-yielding oxidative phenolic coupling as the key step. The intermediate (27) was also converted via a reductive fragmentation into the dibenzazecine (9), oxidation of which gave a dienone different from (12), clearly having the 5;7-fused structure (10). A report of the synthesis of (10) by a different route is thus confirmed, and efficient routes are available to the phenols (9) and (10), likely biosynthetic precursors of the Schelhammera alkaloids.

An alternative cycloaddition approach to the dienone (12) was abandoned when (19) and (25) failed to give Diels–Alder adducts with the oxygenated dienones (20) and (21).