Novel homophthalimide (isoquinoline-1,3-dione) derivatives obtained by addition–cyclisation reactions of nona-2,7-diynedioic acid derivatives with methylamine

Abstract

Reactions of nona-2,7-diynediamide and the corresponding diethyl ester with aqueous methylamine afford the novel imides, 6,7-dihydro-8-methylaminoisoquinoline-1 (2H),3(5H)-dione (V) and its 2-methyl derivative (IV). The properties of these and of various derivatives obtained by replacement of the labile methylamino-group are discussed. Dehydrogenation readily gives the corresponding 6-substituted homophthalimides (isoquinoline-1,3-diones); the structure of the 6-hydroxy-2-methyl compound (XIII) was confirmed by synthesis. The methylamine reaction evidently involves conjugate addition followed by intramolecular cyclisation. Mild treatment of the diacetylenic diester with sodium hydroxide effects a different type of rearrangement, with production of homophthalic acid and 3-ethoxynona-3,5,7-trienedioic acid.