Synthesis and reactions of lithio derivatives of 1‐allenylbenzotriazole

1‐(2‐Chloropropen‐2‐yl)benzotriazole ( 6 ) is converted by heating with sodium hydroxide or by lithium diisopropylamide at ‐78° into 1‐allenylbenzotriazole ( 1 ) in high yield. Allene 1 undergoes in situ lithiation at the α‐carbon and subsequent reactions with iodomethane or carbonyl compounds to produce 1‐(1‐substituted allenyl)benzotriazoles 9 and 2a‐c , respectively. Three equivalents of lithium diisopropylamide dilithiated 1 and afforded symmetrical 1‐(1,3‐disubstituted allenyl)benzotriazoles 11a,b upon reaction with ketones. The unsymmetrical 1‐(1,3‐disubstituted allenyl)benzotriazole 5 was obtained via a stepwise addition of benzophenone to the lithio derivative of 1 followed by a second lithiation and quenching with acetone. Monosubstituted allenes 2a and 8 were cyclized into the benzotriazolyl substituted dihydrofuran 3 and dihydropyrrole 4 respectively.