Direct photolytic and radical induced homolyses of O-alkyl arylaldoxime eth
ers (ArCH=NOR) were studied by EPR spectroscopy and by end product analyses
. Initiating radicals (X-.), including t-BuO., t-BuS., alkyl and Me3Sn., ad
ded rapidly to the C=N double bond to give adduct oxyaminyl radicals ((ArCH
XNOR)-O-.) that could be observed and characterised by EPR spectroscopy. Fo
r O-alkyl arylaldoxime ethers containing H-atoms attached to the carbon adj
acent to the ether oxygen (OR=OCHR21), t-BuO. radicals also abstracted this
hydrogen to yield oxyalkyl radicals that underwent rapid beta-scission to
afford iminyl radicals (ArCHN.) and an aldehyde or ketone ((R2CO)-C-1). As
judged by the relative importance of ROH and ArCN amongst the products, abs
traction of the iminyl hydrogen atom also took place to yield oximidoyl rad
icals (ArC.=NOR), although this could not be confirmed by EPR spectroscopic
observation of these radicals. Thus, homolysis induced by t-BuO. radicals
took place comparatively unselectively. Addition of the t-BuO. radical to t
he C=N double bond of oxime ethers was very fast, the rate constant being c
omparable to that for addition of the same radical to nitrones. Direct and
photosensitised UV photolysis of O-alkyl arylaldoxime ethers gave alkoxyl a
nd aryliminyl radicals in very low yields. Although traces of 2-methyltetra
hydrofuran were detected from cyclisation of the pent-4-enyloxyl radical ge
nerated by direct photolysis of O-pent-4-enyl benzaldoxime, yields were too
low for preparative purposes.