Asymmetric Synthesis of C2-Symmetric Annulated Bicyclooctylcyclopentadienes

All articles of this category The efficient asymmetric preparation of the C 2 -symmetric annulated cyclopentadienes, (+)-(1 R ,7 R ,8 R ,10 R )-8, 10-diisopropyltricyclo[5.2.2.0 2,6 ]undeca-2,5-diene ( 1 ) and (-)-(1 S ,7 S ,8 R ,10 R )-8,10-dimethyltricyclo [5.2.2.0 2,6 ]undeca-2,5-diene( 2 ) is described. The key step in these syntheses is an asymmetric dihydroboration of 1,4-dialkyl-1,4-cyclohexadienes using enantiomerically pure isopinocamphenylborane. The overall yield of enantiomerically enriched 1 or 2 is 27% and 20%, respectively, for the five-step synthesis (Birch reduction of 1,4-dialkylbenzene, asymmetric dihydroboration-oxidation, bis(methanesulfonate) formation, bisalkylation of cyclopentadiene, and [1,5]-sigmatropic rearrangement). The formation of chiral titanocene dichlorides is described.