Chemistry of Unique Chiral Olefins. 3. Synthesis and Absolute Stereochemistry of trans- and cis-1,1‘,2,2‘,3,3‘,4,4‘- Octahydro-3,3‘-dimethyl-4,4‘-biphenanthrylidenes

Abstract

Unique chiral olefins with two methyl groups as the internal reference of absolute stereochemistry, (3R,3‘R)-(P,P)-(E)-(−)-1,1‘,2,2‘,3,3‘,4,4‘-octahydro-3,3‘-dimethyl-4,4‘-biphenanthrylidene (3) and its (3R,3‘R)-(P,P)-(Z)-isomer (4), were synthesized in optically pure form starting from (3R,4R)-(+)-1,2,3,4-tetrahydro-3-methyl-4-phenanthrenol (11), which was obtained by the enantioresolution using a novel chiral auxiliary of dichlorophthalic acid amide (14). The absolute stereochemistry of chiral trans-dimethyl olefin (−)-3 was determined by the X-ray crystallographic analyses of ester (−)-16b and (−)-3 itself. Optically pure cis-dimethyl olefin 4 was prepared by photochemical reaction of trans-olefin (−)-3. The CD spectra of these chiral dimethyl olefins exhibit very intense Cotton effects in the 1Bb transition region reflecting their strongly twisted π-electron systems. The CD spectrum of (3R,3‘R)-(P,P)-(E)-(−)-3 is almost similar in shape but opposite in sign to that of (M,M)-(E)-1,1‘,2,2‘,3,3‘,4,4‘-oct...