converted into the corresponding enantiomerically pure diones 4b, the absoluteconfiguration of which was determined by comparison of the experimental and simulated circular dichroism (CD) spectra, obtained by ab initio time-dependent density functional theory (TDDFT) calculations. The (−)-(1R,5R)/(+)-(1S,5S) absoluteconfiguration of 4b inferred from the TDDFT calculations was confirmed via analysis
Functionalized Bicyclo[3.3.0]octanes by Enantioselective Transannular Desymmetrization
作者:David M. Hodgson、Iain D. Cameron
DOI:10.1021/ol006947n
日期:2001.2.1
alpha-deprotonation-rearrangement of achiral substituted cyclooctene oxides 7, 17, and 18 using organolithiums in the presence of (-)-sparteine (3) or (-)-alpha-isosparteine (4) gives the functionalized bicyclo[3.3.0]octan-2-ols 8, 19, and 20 in 56-72% yields and 83-89% ee's.
Intramolecular Bromonium Ion Assisted Epoxide Ring-Opening: Capture of the Oxonium Ion with an Added External Nucleophile
作者:Karl J. Bonney、D. Christopher Braddock、Andrew J. P. White、Muhammad Yaqoob
DOI:10.1021/jo101617h
日期:2011.1.7
bromonium ion-assisted epoxide ring-opening using N-bromosuccinimide via a presumed oxonium ion that is subject to stereospecific, nonregioselective capture with added external nucleophiles producing novel bicyclo[4.2.1] and bicyclo[3.3.1] ethers. Carboxylic acids (as catalyzed by tetramethylguanidine), alcohols, water, and halides can all function as effective nucleophiles. Stereospecific direct opening
of vellosimine and itsderivatives is secured from a readily affordable C2-symmetric 9-azabicyclo[3.3.1]nonane precursor available in both enantiomeric forms. The strategy reported leverages desymmetrization via intramolecular cyclization used to assemble the key intermediate with two differentiated carbonyl groups. Late-stage site selective indolization enables a concise synthesis of vellosimines and