Mono- and diorganotin derivatives of (S)-BINOL diesters as precursors of C₂ symmetry chiral catalysts

The aim of this work is the synthesis of some BINOL derivatives due to their catalytic, biological and medicinal activity. The rigid structure, thermal stability and the C₂ symmetry of the binaphthyl molecules play an important rol in asymmetric induction. We report here a study on the radical addition of different triorganotin hydrides, R3SnH (R= n-Bu, Ph), to four (S)-BINOL unsaturated diesters (1,1'-binaphthyl-2-2´-diyl diacrylate; 1,1´-binaphthyl-2-2´-diyl dimethacrylate; 1,1´-binaphthyl-2-2´-diyl-(Z)-2-methyl-3-phenyl-2- propenoate and 1,1´-binaphthyl-2-2´-diyl di-(Z)-2,3-diphenyl-2-propenoate). The expected cyclohydrostannation products were not obtained in spite of the different conditions used for the reaction: sonication, irradiation and refluxing in toluene, with AIBN as radical initiator. This probably occurred due to the restricted conformational structure of the BINOL diesters. Rather than cyclization products, the corresponding mono- and diorganotin adducts were the mainly products obtained under radical addition of the tin hydrides. These organotin adducts can be easily derived in halotrialkyltin or halodialkylaryltin compounds, some of them with probable catalytic activity. For example, organotin halides are Lewis acids so they can be used as catalysts in different reactions, such as asymmetric Diels-Alder cycloaddition and alcohol acylations among others, where the metal catalytic centre is near the chiral binaphthyl moiety. Some authors have demonstrated that diorganotindihalides has higher catalytic effect compared to triorganotin halides and similar to geminal bis(haloorganostannanes). We studied the relation between mono and distannilated products and the diasteroselectivity in appropiate cases. These compounds were characterized with 1H, 13C and 119Sn-NMR.