The crystal structure, absolute configuration, and circular dichroism of (R)-(–)546-8,8′-(2-thiatrimethylene)-1,1′-binaphthyl

Abstract

The crystal structure of (–)546-(2-thiatrimethylene)-1,1′-binaphthyl has been examined by the Bijvoet X-ray method using Cu radiation: the orthorhombic crystals are of space group P212121 with four molecules in a unit cell of dimensions a= 8.442(7), b= 9.491(3), c= 20.075(9)A. The structure was solved using MULTAN, and refined to a final R value of 2.3%. The molecules are found to have axial chirality R(helicity M), while each individual naphthalene unit is twisted with P helicity. The angle between the main planes of the naphthalene pairs is 92.5° and they are badly buckled, as predicted earlier on the basis of the low optical stabilities of related but unbridged compounds. The pattern of naphthalene bond lengths is unusual, all bonds adjacent to the strained points of connection of two naphthalene rings to each other and to the 2-thiatrimethylene bridge being longer than normal. The two six-membered rings adjacent to the 2-thiatrimethylene bridge are more distorted from planarity than the other two. The C–S and C–C bond lengths in the bridge average 1.830 and 1.496 A, while the naphthyl–naphthyl C–C distance is 1.503 A. The C–S–C angle is 103.8°. C.d. spectra of this and related compounds are presented, compared, and discussed. Chemical correlation through synthesis extends the assignment of absolute configuration to many other 8,8′-disubstituted 1,1′-binaphthyls.