Nucleophilic Attack on 4,5-Dihydro-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

Abstract

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 corresponding 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 coun- terions favor formation of bidentate ligands (7). An explanation based on a competition between the counterion and the external nucleophile is provided. Dihydrothiepinium salts (6) are easily accessible from dibro- mide (R,S)-(4) via dihydrothiepin (R,S)-5. Individual enantiomers (R)- and (S)-(5) have been obtained by resolution on a preparative triace- tylcellulose (TAC) column ans assigned absolute configuration on the basis of CD spectra and chemical correlation