Tin triflate-mediated total synthesis of circumdatin F, sclerotigenin, asperlicin C, and other quinazolino[3,2-a][1,4]benzodiazepines

Using tin triflate, as an effective Lewis acid, and microwaves, direct double cyclizations of bis(anthranilate)-containing tripeptide precursors to afford the total syntheses of 7-substituted quinazolino[3,2-a][1,4]benzodiazepinediones (1a-f), including natural products circumdatin F (1a), sclerotigenin (1b), and asperlicin C (1c), were achieved with good overall isolated yields (23-62%).