PHOTOSTIMULATED REACTIONS OF O-DIHALOBENZENES WITH NUCLEOPHILES DERIVED FROM THE 2-NAPHTHYL SYSTEM - COMPETITION BETWEEN ELECTRON-TRANSFER,FRAGMENTATION, AND RING-CLOSURE REACTIONS

The photostimulated reaction of o-dihalobenzenes 2 with 2 naphthoxide ions 1-O gave the substitution product on carbon 1 of the naphthyl moi ety with retention of halogen (1, Br, and Cl) 3 as well as the ring cl osure product benzo[b]naphtho[1,2-d]furan (4), with product 3 being an intermediate in the formation of 4. The products obtained in the phot ostimulated reaction of 2-naphthalenethiolate ions 1-S with 2 depend o n the halogens. When both nucleofugal groups are iodine, only the ring closure product benzo[b]naphtho[1,2-d]thiophene (10) is obtained. Wit h o-bromoiodobenzene, the photostimulated reaction gave 10 and the sub stitution product on sulfur with retention of bromine, while with o-ch loroiodobenzene the only observed product was the substitution product on sulfur with retention of chlorine. The photostimulated reaction of 2 with 2-naphthaleneselenolate ions 1-Se gave the same amount of cycl ized product benzo[b]naphtho[1,2-d]selenophene (14) and the substituti on product on selenium without retention of halogen 15, although in an overall low yield. It is suggested that all these reactions occur by the S(RN)1 mechanism. Theoretical studies support the different behavi or found with the nucleophiles derived from the 2-naphthyl system.