Add time:07/22/2019         Source:sciencedirect.com

The synthesis of chiral tricyclo[4.3.0.03,8]nonane-4,5-dione was accomplished starting from enantiomerically pure (+)-(1S,5S)-bicyclo[3.3.1]nonane-2,6-dione 1. Ring contraction of the latter with thallium(III) nitrate proceeded with high stereoselectivity giving exclusively methyl (+)-(1S,4S)-(+)-exo,exo-bicyclo[2.2.1]heptan-2,5-dicarboxylate 2. Inversion of the configuration of this diester to the required di-endo derivative was realized via the following reaction sequence. Bromination of the corresponding acid dichloroanhydride and subsequent reduction with zinc in acetic acid gave a diastereoisomeric mixture of esters, from which the endo,endo-ester 5 was isolated by column chromatography. Acyloin condensation of the latter with trimethylchlorosilane in toluene led to intramolecular ring closure, and subsequent oxidation of the enol silyl ether 7 in situ gave tricyclo[4.3.0.03,8]nonane-4,5-dione 8. The chiroptical properties of this cage molecule were studied by electronic and vibrational circular dichroism spectroscopy. The (1R,3R,6R,8R) absolute configuration of the title structure was also unambiguously proved.

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