Diazo-Transfer Reaction with Diphenyl Phosphorazidate

✍ Scribed by José M. Villalgordo; Adelheid Enderli; Anthony Linden; Heinz Heimgartner

• Publisher: John Wiley and Sons
• Year: 1995
• Tongue: German
• Weight: 878 KB
• Volume: 78
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19950780807

✦ Synopsis

Abstract

Diphenyl phosphorazidate (DPPA) was used as the azide source in a one‐pot synthesis of 2,2‐disubstituted 3‐amino‐2__H__‐azirines 1 (Scheme 1). The reaction with lithium enolates of amides of type 2, bearing two substituents at C(2), proceeded smoothly in THF at 0°; keteniminium azides C and azidoenamines D are likely intermediates. Under analogous reaction conditions, DPPA and amides of type 3 with only one substituent at C(2) gave 2‐diazoamides 5 in fair‐to‐good yield (Scheme 2). The corresponding 2‐diazo derivatives 6–8 were formed in low yield by treatment of the lithium enolates of N,N‐dimethyl‐2‐phenylacetamide, methyl 2‐phenylacetate, and benzyl phenyl ketone, respectively, with DPPA. Thermolysis of 2‐diazo‐N‐methyl‐N‐phenylcarboxamides 5a and 5b yielded 3‐substituted 1,3‐dihydro‐N‐methyl‐2__H__‐indol‐2‐ones 9a and 9b, respectively (Scheme 3). The diazo compounds 5–8 reacted with 1,3‐thiazole‐5 (4__H__)‐thiones 10 and thiobenzophenone (13) to give 6‐oxa‐1,9‐dithia‐3‐azaspiro[4.4]nona‐2,7‐dienes 11 (Scheme 4) and thiirane‐2‐carboxylic acid derivatives 14 (Scheme 5), respectively. In analogy to previously described reactions, a mechanism via 1,3‐dipolar cycloaddition, leading to 2,5‐dihydro‐1,3,4‐thiadiazoles, and elimination of N~2~ to give the ‘thiocarbonyl ylides’ of type H or K is proposed. These dipolar intermediates with a conjugated CO group then undergo either a 1,5‐dipolar electrocyclization to give spirohetrocycles 11 or a 1,3‐dipolar electrocyclization to thiiranes 14.