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On the Origin of Regio- and Stereoselectivity in Singlet Oxygen Addition to Enecarbamates

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Title On the Origin of Regio- and Stereoselectivity in Singlet Oxygen Addition to Enecarbamates
 
Creator RAJEEV, R
SUNOJ, RB
 
Subject DENSITY-FUNCTIONAL THEORY
DIASTEREOSELECTIVE DIOXETANE FORMATION
MULTIREFERENCE PERTURBATION-THEORY
ASYMMETRIC ALDOL REACTIONS
TRANSITION-METAL DIMERS
CHIRAL ALLYLIC ALCOHOLS
ENE REACTION
2+2 CYCLOADDITION
MOLECULAR-OXYGEN
PEREPOXIDE INTERMEDIATE
 
Description The reactions of excited state singlet molecular oxygen ((1)Delta(g), O-1(2)) continue to witness interesting new developments. In the most recent manifestation, O-1(2) is tamed to react with enecarbamates in a stereoselective manner, which is remarkable, in view of its inherently high reactivity (Acc. Chem. Res. 2008, 41, 387). Herein, we employed the CAS-MP2(8,7)/6-31G* as well as the CAS-MP2(10,8)/6-31G* computations to unravel the origin of (i) diastereoselectivities in dioxetane or hydroperoxide formation and (ii) regioselectivity leading to a [2 + 2] cycloadduct or an ene product when O-1(2) reacts with an oxazolidinone tethered 2-phenyl-1-propenyl system. The computed Gibbs free energy profiles for E- and Z-isomers when O-1(2) approaches through the hindered and nonhindered diastereotopic faces (by virtue of chiral oxazolidinone) of the enecarbamates exhibit distinct differences. In the case of E-isomer, the relative energies of the transition structures responsible for hydroperoxide (ene product) are lower than that for dioxetane formation. On the other hand, the ene pathway is predicted to involve higher barriers as compared to the corresponding dioxetane pathway for Z-isomer. The energy difference between the rate-determining diastereomeric transition structures involved in the most favored ene reaction for E-enecarbamate suggests high diastereoselectivity. In contrast, the corresponding energy difference for Z-enecarbamate in the ene pathway is found to be diminishingly close, implying low diastereoselectivity. However, the dioxetane formation from Z-enecarbamate is predicted to exhibit high diastereoselectivity. The application of activation strain model as well as the differences in stereoelectronic effects in the stereocontrolling transition structures is found to be effective toward rationalizing the origin of selectivities reported herein. These predictions are found to be in excellent agreement with the experimental observations.
 
Publisher AMER CHEMICAL SOC
 
Date 2014-10-15T12:22:21Z
2014-10-15T12:22:21Z
2012
 
Type Article
 
Identifier JOURNAL OF ORGANIC CHEMISTRY, 77(5)2474-2485
http://dx.doi.org/10.1021/jo3001707
http://dspace.library.iitb.ac.in/jspui/handle/100/14893
 
Language en