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A Study of Vinyl Radical Cyclization onto the Azido Group by Addition of Sulfanyl, Stannyl, and Silyl Radicals to Alkynyl Azides ☆
Author(s) -
Montevecchi Pier Carlo,
Navacchia Maria Luisa,
Spagnolo Piero
Publication year - 1998
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/(sici)1099-0690(199806)1998:6<1219::aid-ejoc1219>3.0.co;2-v
Subject(s) - sulfanyl , chemistry , radical , alkyl , radical cyclization , azide , medicinal chemistry , silylation , triple bond , double bond , polymer chemistry , organic chemistry , catalysis
Thermal radical reactions of azidoalkynes 2 , 8 , 14 , and 21a–c with thiols 1a–c afford 2‐sulfanylvinyl radicals by selective addition of sulfanyl radicals to the triple bond. 1‐Phenylvinyl radicals 23 and 30a , as well as vinyl radical 30b , undergo fast 5‐cyclization onto the aromatic azide function to give cyclized indoles. In contrast, both 1‐phenyl ( 15 , 17 ) and 1‐alkyl ( 3a , b , 9 ) vinyl radicals fail to add to their aliphatic azido substituents and exclusively undergo cyclization onto the aromatic sulfanyl ring and H transfer from the thiol precursor. Azidoalkynes 14 and 21a react with Bu 3 SnH and TMSS under radical conditions to give instead the corresponding amines as a result of preferential attack of Bu 3 Sn · and (TMS) 3 Si · radicals on the azido group rather than on the triple bond. Evidence is provided that alkyl radical cyclizations onto azides are not feasible in the presence of thiol, in contrast with the reported utility of these cyclization reactions in the presence of Bu 3 SnH and TMSS.