Diazo-Transfer Reaction with Diphenyl Phosphorazidate

Article abstract of DOI:10.1002/hlca.19950780807

Diphenyl phosphorazidate (DPPA) was used as the azide source in a one-pot synthesis of 2,2-disubstituted 3-amino-2H-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 degree C; 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-subdtituted 1,3-dihydro-N-methyl-2H-indol-2-ones 9a and 9b, respectively (Scheme 3).The diazo compounds 5-8 reacted with 1,3-thiazole-5(4H)-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 N2 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 spiroheterocycles 11 or a 1,3-dipolar electrocyclization to thiiranes 14.