Spin Adducts from the Reaction Between N-Phenyl-alpha-tert-butylnitrone (PBN) and Activated Olefins. A Facile Pathway Converting PBN into 2-Methyl-2-nitrosopropane (MNP).
作者:Lennart Eberson、Ola Persson、Kjartan Marøy、Alexander Krivokapic、Frode Rise、Anniken T. Øverås、Teófilo Rojo
DOI:10.3891/acta.chem.scand.52-1081
日期:——
N-Phenyl-alpha-tert-butylnitrone (PBN) reacts with activated olefins RCH=CHR, such as maleimides, maleic anhydride or diethyl maleate, with formation of two types of persistent spin adducts giving characteristic EPR spectra, denoted types A and B. Spin adducts with type A spectrum were formed photochemically and identified as reductive coupling products between the olefin and PEN, RCH2CH(R)-PBN.. Spin adducts with type B spectra were formed photochemically and/or thermally and were identified as reductive coupling products RCH2CH(R)-N(O-.)Bu-t between the olefin and a degradation product of PEN, 2-methyl-2-nitrosopropane (MNP, t-BuNO).The conversion of PEN to t-BuNO was studied for a compound with an exceedingly reactive nitrogen-nitrogen double-bond, namely 4-phenyl-4H-1,2,4-triazoline-3,5-dione (PTAD). In this case, a 74% yield of t-BuNO was obtained in a short period of time; alpha,N-diphenylnitrone reacted similarly to give nitrosobenzene. The reaction between PEN and an activated olefin was assumed to occur analogously, either via the initial formation of a 1,3-dipolar cycloadduct or some parallel reaction involving attack of the electrophilic olefin at the PEN a-carbon. The 1,3-dipolar cycloadduct between PEN and N-phenylmaleimide exhibited favourable initiator properties for living polymerization of styrene.A new type of spin adduct, RCH(Bu-t)CH(R)-N(O-.)Bu-t, was prepared by the photochemical reaction between an activated olefin and t-BuNO. This reaction presumably proceeds by photocleavage of t-BuNO to NO and t-Bu-., the latter reacting with the activated olefin to give a transient radical, RCH(Bu-t)CH.(R), which is trapped by t-BuNO.