Rearrangements of pyrimido- and diazepino-[1,2-a]indoles: syntheses of 1,5-benzodiazocines and 1,6-benzodiazonines

Abstract

Rearrangements of the pyrimido[1,2-a]indoles 1 and 2 and the pyrimido[1,2-a]indolinium iodide 13 produce the 1,2,3,4,5,6-hexahydro-1,5-benzodiazocines 7–9. The diazepino[1,2-a]indole 16 produces the 2,3,4,5,6,7-hexahydro-1,6-benzodiazonine 18. Formation of compounds 7 and 8 is less facile than that of compounds 9 and 18. The pyrimido[1,2-a]indoles 1 and 2 and the diazepino[1,2-a]indole 16 undergo rearrangement with arenesulphonyl chlorides such as toluene-p-sulphonyl chloride but not with carboxylic acid chlorides to give the diazocines 10 and 12 and the diazonine 20. Mechanisms for the rearrangements are discussed in terms of indole 2,3-oxide intermediates. The reduction of the pyrimido[1,2-a]indole 2 with lithium tetrahydroaluminate generates the bicyclic aminal 26. The treatment of the bicyclic lactam 11 with lithium tetrahydroaluminate or with sodium methoxide results in ring-opening and formation of the 1,2,3,4-tetrahydro- and 1,2,3,4,5,6-hexahydro-1,5-benzodiazocines 27 and 28.