Total Synthesis of (-)-Chokol A by an Asymmetric Domino Michael Addition-Dieckmann Cyclization
作者:Ulrich Groth、Christian Kesenheimer、Paul Kreye
DOI:10.1055/s-2006-949653
日期:2006.9
A convergent and asymmetric total synthesis of (-)- chokol A was accomplished in six steps starting from the a,b-unsat- urated ester (E)-9 in an overall yield of 27% with an enantiomeric excess of 95%. The key step of this synthesis is the asymmetric tandem conjugate addition-Dieckmann cyclization of the higher- order cuprate 8 derived from vinyl bromide 7 with the a,b-unsatur- ated ester (E)-9.
Total synthesis of (±)chokol-A via an intramolecular type-I-magnesium ene reaction.
作者:Wolfgang Oppolzer、Allan F. Cunningham
DOI:10.1016/s0040-4039(00)85239-9
日期:1986.1
The sesquiterpene (±)chokol-A () was synthesized in a diastereoselective manner starting from 1-hexen-5-one-trisylhydrazone (). The key step → involves the regio- and stereo-selective magnesium-ene reaction → .
(-)-Chokol A (10) was prepared in six steps (22% overall yield) via conjugate addition of a higher order cyanocuprate to the chiral 2-oxo-cyclopentenecarboxylate 2n After deprotection by transesterification the enantiomerically pure β-ketoester 5 was obtained which was transformed by α-methylation and subsequent decarbethoxylation to the cyclopentanone derivative 8. Addition of methylcerium dichloride
New fungitoxic sesquiterpenes, chokol A (1), B (2), and C (3), have been isolated from stromata of . Their structures and the relative configuration of 3 have been also elucidated from spectral data.