Synthesis and structure verification of an analogue of kuanoniamine A

Abstract

Synthesis of 9-phenyl-7H-benzothiazolo[4,5,6-ij][2,7]naphthyridin-7-one 11, an analogue of kuanoniamine A 8, is described. The synthesis involves a hetero Diels–Alder reaction of crotonaldehyde dimethylhydrazone with 4,7-dioxo-2-phenylbenzothiazole 18a or with 6-bromo-4,7-dioxo-2-phenylbenzothiazole 18b followed by annelation of the appropriate adduct. Reaction with 18a produced two sets of regioisomers—the thiazoloquinolinediones 19a,b, and the dimethylamino dioxobenzothiazoles 23a,b. The structure of 23b was determined by single-crystal X-ray structure analysis. Verification of the other structures, and methods used to improve the Diels–Alder reaction are described.