The commercially important isochromane musk odorant Galaxolide® (=1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethylcyclopenta[g]-2-benzopyran; HHCB; 3) was separated into its diastereoisomers via the tricarbonyl(η6-cyclopenta[g]-2-benzopyran)chromium complexes 10. Since GC/olfactometry indicated that only one enantiomer of each diastereoisomer (4RS,7RS)-3 and (4RS,7SR)-3 determines the odor characteristics of the commercial product, all four stereoisomers (4S,7R)-, (4S,7S)-, (4R,7S)-, and (4R,7R)-3 were synthesized by Friedel-Crafts alkylation of 1,1,2,3,3-pentamethylindane (11) with (S)- and (R)-methyloxirane ((S)- and (R)-12, resp.), acid-catalyzed reaction of the resulting products with paraformaldehyde, and separation of the formed diastereoisomer pairs via the tricarbonyl(η6-cyclopenta[g]-2-benzopyran)chromium complexes 10. The powerful musk odor of Galaxolide ® (3) was thus attributed to its (−)-(4S)-isomers (4S,7R)- and (4S,7S)-3, while the (+)-(4R)-isomers (4R,7S)- and (4R,7R)-3 were weak to almost odorless.
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Fráter et al. (1999) studied this question.