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

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 B-1(b) transition region reflecting their strongly twisted pi-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'-octahydro-4,4'-biphenanthrylidene (1). Therefore, the absolute stereochemistry of (M,M)-(E)-1 previously theoretically determined was established in an experimental manner. The CD spectrum of (3R,3'R)-(P,P)-(Z)-4 is also almost similar in shape but opposite in sign to that of (M,M)-(Z)-1,1',2,2',3,3',4,4'-octahydro-4,4'-biphenanthrylidene (2). The absolute stereochemistry of (M,M)-(Z)-2 theoretically determined was corroborated.