op-1-ene-3,3,3-d(3) (trans-5-d(3)) to C(60) is attributed to a steric kinetic isotope effect (k(H)/k(D) = 0.78). The loss of stereochemistry in the cyclobutane ring excludes a concerted addition and is consistent with a stepwisemechanism. Intermolecular secondary kinetic isotopeeffects of the [2 + 2] photocycloaddition of 3-d(0) vs 3-d(1), and 3-d(6) as well as 5-d(0) vs 5-d(1), and 5-d(6) to C(60)
Stereoelectronic and solvent effects on the allylic oxyfunctionalization of alkenes with singlet oxygen
作者:Mariza N. Alberti、Michael Orfanopoulos
DOI:10.1016/j.tet.2006.07.106
日期:2006.11
control the stereochemistry of sensitized photooxygenation of alkenes via singletoxygen (enereaction) are selectively reported. We also introduce our most recent stereoelectronic effects on the singlet oxygen–ene reaction. The origin of site selectivity and solvent-dependent stereoselectivity in this classical enereaction with simple as well as functionalized alkenes is highlighted. These studies
Stereochemistry and steric isotope effect on the [2+2] photocycloaddition of β,β-dimethyl-p-methoxystyrene to C60: the nature of the transition state structures
The photochemical [2+2] cycloaddition of β,β-dimethyl-p-methoxystyrene to C60 occurs with loss of stereochemical integrity. The substantial remote kinetic isotope effect in the title reaction, indicates the formation of an open, relatively long lived intermediate.
Control of Regioselectivity by the <i>l</i><i>one</i> Substituent through Steric and Electronic Effects in the Nitrosoarene Ene Reaction of Deuterium-Labeled Trisubstituted Alkenes
For the enereaction of 4-nitronitrosobenzene (ArNO) with a variety of primary and secondary lone alkyl-substituted substrates, the twix/twin regioselectivity is constant at about 85:15. In contrast, for the lone tert-butyl group and for lone aryl substituents, the twix regioisomer is obtained exclusively. These regioselectivities have been rationalized in terms of steric interactions and coordination
Electronic effects in the regioselectivity of the singlet oxygen and 4-methyl-1,2,4-triazoline-3,5-dione ene reactions with isobutenylarenes
作者:Mariza N. Alberti、Georgios C. Vougioukalakis、Michael Orfanopoulos
DOI:10.1016/s0040-4039(02)02783-1
日期:2003.1
The regioselectivity of the ene pathway in the photooxidation of several 1-aryl-2-methylpropenes, as probed by stereoselective deuterium-labeling, depends on the electronic nature of the para phenyl-substituents. The reaction of the same array of alkenylarenes with 4-methyl-1,2,4-triazoline-3,5-dione (MTAD) gives ene products with an impressive >97% allylic hydrogen abstraction from the more substituted