Reaction of a Stable Conjugated Primary Enamine with Piers' Borane

Abstract

Abstract Treatment of 1,6‐diamino‐1,6‐diphenyl‐1,3,5‐hexatriene ( 3 ) with 2 mol‐equiv. of HB(C 6 F 5 ) 2 results in tautomerization of the stable primary enamine to its bis(imine) tautomer, which is stabilized by twofold imine/borane Lewis base/Lewis acid adduct formation to yield an 11:6:1 mixture of E , E ‐ 5 , E , Z ‐ 5 and Z , Z ‐ 5 . Within several hours at room temperature, these systems undergo subsequent hydroboration of the central remaining C=C double bond followed by internal imine–alkylborane coordination to yield the six‐membered N,B heterocycle 6 featuring a pendant –CH 2 –C(Ph)=NH[B(H)(C 6 F 5 ) 2 ] group. Compound 6 was characterized by X‐ray diffraction.