Interception and Synthetic Application of Diradical and Diene Forms of Dual-Nature Azabicyclic o-Quinodimethanes Generated by 6p-Azaelectrocyclization.

We demonstrate that 2-alkenylarylaldimines and ketimines undergo thermal 6p-azaelectrocyclization to generate a wide range of azabicyclic o-quinodimethanes (o-QDMs). These o-QDMs exist as a hybrid of a diene and a benzylic diradical. The diradical nature was confirmed by their ability to undergo dimerization and react with H-atom donor, 2,2,6,6-Tetramethylpiperidin-1-yl)oxyl (TEMPO) and O2. In addition, the interception of the diradicaloid o-QDMs by H-atom transfer was used to synthesize five tetrahydroisoquinoline alkaloids and related bioactive molecules. The diene form can undergo [4 + 2] cycloaddition reactions with different dienophiles to generate bridged azabicycles in high endo:exo selectivity. The azabicyclic o-QDMs can be generated for [4 + 2] cycloaddition from a wide range of electronically and sterically varied 2-alkenylarylimines, including mono, di, tri and tetrasubstituted alkenes, and imines derived from arylamine, alkylamine (1°, 2°, 3°), benzylamine, benzylsulfonamide and Boc-amine.

α-Bromoacetate as a Mild and Safe Brominating Agent in the Light-Driven Vicinal Dibromination of Unactivated Alkenes and Alkynes.

Light-induced vicinal dibromination of unactivated alkenes and alkynes has been demonstrated by using methyl α-bromoacetate as a mild brominating agent. A near-visible light (370 nm) light-emitting diode (LED) mediates this simple dibromination reaction under mild conditions with the inexpensive and nontoxic α-bromoacetate. The reaction proceeds well with both terminal and internal alkenes and alkynes and those contained in N/O-heterocycles, indicating its versatility in synthesizing dibrominated organic compounds.