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 moiety with retention of halogen (1, Br, and Cl) 3 as well as the ring closure 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 photostimulated reaction of 2-naphthalenethiolate ions 1-S with 2 depend on the halogens. When both nucleofugal groups are iodine, only the ring closure product benzo[b]naphtho[1,2-d]thiophene (10) is obtained. With o-bromoiodobenzene, the photostimulated reaction gave 10 and the substitution product on sulfur with retention of bromine, while with o-chloroiodobenzene 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 cyclized product benzo[b]naphtho[1,2-d]selenophene (14) and the substitution 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 behavior found with the nucleophiles derived from the 2-naphthyl system.