Cascade Synthesis of Pyrrolo[1,2-]quinolines and Pyrrolo[2,1-]isoquinolines via Formal [3 + 2]-Cycloaddition of Push-Pull Nitro Heterocycles with Carbonyl-Stabilized Quinolinium/Isoquinolinium Ylides.

Various substituted pyrrolo[1,2-]quinolines and pyrrolo[2,1-]isoquinolines were synthesized in good to high yields by the EtN-mediated reaction of push-pull 3-nitrobenzofurans or 1-Ts-/1-Ms-3-nitroindoles and precursors of carbonyl-stabilized quinolinium and isoquinolinium ylides as 1,3-dipole equivalents. These transformations proceed in a one-pot manner starting with the formal [3 + 2]-cycloaddition stage, which is accompanied by double dearomatization of both quinoline/isoquinoline and benzofuran/indole moieties, followed by ring-opening of cyclic intermediate formed and nitrous acid elimination sequence. [3 + 2]-Cycloadducts were isolated as the final products in cases of impossibility or difficulty of their enolization.

An Inverse Electron Demand Azo-Diels-Alder Reaction of o-Quinone Methides and Imino Ethers: Synthesis of Benzocondensed 1,3-Oxazines.

We have studied the reactions of o-quinone methide precursors with imino ethers. The reaction provides a versatile route to substituted 1,3-benzoxazines. The proposed reaction mechanism involves the generation of the o-quinone methide intermediates, imino-Diels-Alder reaction, and elimination.