NUCLEOPHILIC-ATTACK ON YDRO-4-ALKYL-3H-DINAPHTHO[2,1-C-1',2'-E]THIEPINIUM SALTS - A CONVENIENT APPROACH TO NEW 2,2'-BIDENTATE 1,1'-BINAPHTHALENE LIGANDS WITH SULFUR DONOR ATOMS

The title dihydrothiepinium salts 6 react with a wide range of N-, S-, Se-, O-, and C-nucleophiles to afford dihydrothiepin 5 and/or the cor responding bidentate ligands 7. The dual course of the reaction can be controlled by a judicious choice of the substrate counterion. In most instances, an iodide counterion aids formation of dihydrothiepins 5, whereas perchlorate, tetraphenyl borate, or tetrafluoroborate counteri ons favor formation of bidentate ligands 7. An explanation based on a competition between the counterion and the external nucleophile is pro vided. Dihydrothiepinium salts 6 are easily accessible from dibromide (R,S)-4 via dihydrothiepin (R,S)-5. Individual enantiomers (R)- and (S )-5 have been obtained by resolution on a preparative triacetylcellulo se (TAC) column and assigned absolute configuration on the basis of CD spectra and chemical correlation.