addition of the very reactive metallacarbene intermediate in an early transition state to the substrate alkene is concerted but strongly asynchronous, with substantial cationic character on one alkene carbon in the neighborhood of the transition state. Evidence from isotope effects and Hammett studies supports the nature of the transition state. Formation of a metallacyclobutaneintermediate by a [2+2] addition
Tropic acid biosynthesis: the incorporation of (RS)-phenyl[2-18O,2-2H]lactate into littorine and hyoscyamine in Datura stramonium
作者:Chi W. Wong、David O’Hagan、Chi W. Wong、John T. G. Hamilton、David O’Hagan、Richard J. Robins、Richard J. Robins
DOI:10.1039/a801722k
日期:——
The incorporation of oxygen-18 from (RS)-phenyl- [2-18O,2-2H]lactate into the tropane alkaloids littorine 1 and hyoscyamine 2 in Datura stramonium reveals that up to 29% of the oxygen-18 is lost during the transformation of 1 to 2.
Alkene migration to the end-terminal carbon bearing a phenyl group over a chiral siloxy carbon center in Heck reaction
作者:Akiko Ida、Naoyuki Hoshiya、Jun'ichi Uenishi
DOI:10.1016/j.tet.2015.03.018
日期:2015.9
The Heck reaction of aryl bromide with a terminal alkene substrate having a chiral center at the allylic position and a phenyl substituent at another terminal carbon is reported. An alkene migration to the phenyl-substituted end carbon is observed, along with the typical Heck reaction. This zipper-type migration occurs through multiple internal carbon bonds, and the stereochemistry of the internal
Using secondary alpha deuterium kinetic isotope effects to determine the stereochemistry of an E2 reaction; the stereochemistry of the E2 reaction of 1-chloro-2-phenylethane with potassium <i>tert</i>-butoxide in <i>tert</i>-butyl alcohol
作者:Peter James Smith、David AJ Crowe、Kenneth Charles Westaway
DOI:10.1139/v01-086
日期:2001.7.1
Isotopic labelling studies have shown that the E2 reaction of 1-chloro-2-phenylethane with potassium tert-butoxide in tert-butyl alcohol occurs via an anti-periplanar stereochemistry. This demonstrates that the different secondary alpha deuterium kinetic isotopeeffects found for the high and low base concentrations and in the presence of 18-crown-6 ether are because of changes in transition state
Incorporation of deuterium-labelled analogs of isopentenyl diphosphate for the elucidation of the stereochemistry of rubber biosynthesis
作者:Andrew A. Scholte、John C. Vederas
DOI:10.1039/b515750a
日期:——
prepared to investigate the detailed stereochemicalcourse of addition of C5 units during rubber biosynthesis in Hevea brasiliensis and Parthenium argentatum. These analogs were incorporated into the cis-polyisoprene chain by rubber transferase in rubber particles, and the stereochemistry was determined by 2H-NMR analysis of the polymer or of levulinic acid derivatives obtained from its ozonolytic degradation