Bu3SnH-mediated cyclopropyl radical cyclizations onto indole-3-carbaldehyde

1-[ω-(2-Bromocyclopropyl)alkyl]-1H-indole-3-carbaldehydes and benzimidazole analogues were obtained in ~80% yield via the decomposition of Barton ester intermediates. The bromoindolecarbaldehydes were precursors for Bu3SnH-mediated five- and seven-membered cyclopropyl radical intramolecular aromatic substitutions giving cyclopropane-fused adducts in ~55% yields. The cyclization yields are greater than via the direct decomposition of the Barton esters. X-ray crystal structures of 1-[(2-bromocyclopropyl)-trans-methyl]-1H-benzimidazole,
1,1a,2,8b-tetrahydrocyclopropa[3,4]pyrrolo[1,2-a]indole-8-carbaldehyde and 1,1a,2,3,4,10b-hexahydrocyclopropa[3,4]azepino[1,2-a]indole-10-carbaldehyde are included.