Alternative synthesis of 6-(3-methoxybenzyl)pyrazin-2(1H)-one. Synthesis of indeno[1,2-b]pyrazin-2-ones. Crystal structures of 5-acetoxy-1-benzyl-4-tert-butoxycarbonyl-6-(3-methoxybenzylidene)piperazin-2-one, 1-benzyl-4-tert-butoxycarbonyl-7-methoxy-1,3,4,4a-tetrahydroindeno[1,2-b]pyrazin-2-one and 1-benzyl-4-tert-butoxycarbonyl-7-methoxy-1,3,4,9-tetrahydroindeno[1,2-b]pyrazin-2-one

Abstract

1-Acetyl-3-(3-methoxybenzylidene)piperazine-2,5-dione 7a was converted via a 7-step sequence into 6-(3-methoxybenzyl)pyrazin-2(1H)-one 2a. Treatment of 1-benzyl-4-tert-butoxycarbonyl-5-hydroxy-6-(3-methoxybenzylidene)piperazin-2-one 8a with acids results in cyclisation to indeno[1,2-b]pyrazin-2-ones, 9a, 9b or 11. The X-ray crystal structure determinations of 5-acetoxy-1-benzyl-4-tert-butoxycarbonyl-6-(3-methoxybenzylidene)piperazin-2-one, 8b, 1-benzyl-4-tert-butoxycarbonyl-7-methoxy-1,3,4,4a-tetrahydroindeno[1,2-b] pyrazin-2- one, 9b and 1-benzyl-4-tert-butoxycarbonyl-7-methoxy-1,3,4,9-tetrahydroindeno[1,2-b] pyrazin-2-one, 11 are described.