Chiral 1,8-bis(tert-butylphenylphosphino)naphthalene oxides and sulfides: resolution and structures

Abstract Chiral racemic 1,8-bis( tert -butylphenylphosphino)naphthalene oxide ( 2a ) was resolved into enantiomers by fractional crystallization of its diastereomeric adducts 3a with (+)-(2 S ,3 S )-di- O -benzoyl tartaric acid (DBTA), followed by neutralization. Racemic 1,8-bis( tert -butylphenylphosphino)naphthalene ( 1a ) was oxidized with sulfur to two isomers of 1,8-bis( tert -butylphenyl-phosphino)naphthalene monosulfide, rac - 4a and rac - 4a ′, or 1,8-bis( tert -butylphenylphosphino)naphthalene disulfide, rac - 5a . The compounds were characterized by NMR spectroscopy ( 1 H, 31 P, 13 C). Crystal structures were determined by the X-ray method for (−)- 3a, rac - 4a , rac - 4a ′ and rac - 5a ; this allowed the determination of the absolute configuration ( S , S ) for the more soluble adduct (−)- 3a . It was found that rac - 1a undergoes partial epimerization in boiling xylene to give the meso form.