Accentuation of di-.pi.-methane reactivity by central carbon substitution. Mechanistic and exploratory organic photochemistry. LXXV

Synthetic Aspects of the Di-π-methane Rearrangement

“…This interpretation is in agreement with similar increases in efficiency and triplet reactivity promoted by phenyl substitution at the methane carbon, observed by Zimmerman in the DPM process. 19,43,145,148 An intriguing observation in this study is that aldehyde 171 undergoes the ODPM rearrangement while the analogous methyl ketone 70 does not react in this mode. This is the first example of such a situation and, therefore, it opens the possibility of observing ODPM reactions in other aldehydes with substitution patterns similar to ketones that do not undergo the rearrangement.…”

Studies on the scope of the aza-di-π-methane rearrangement of β,γ-unsaturated imines

“…The sample was taped to the immersion well (Pyrex filter) of the conventional apparatus and irradiated for 4 h. After irradiation the solvent was removed to yield a white solid which crystallized from ethanol to afford 1,1,3,3-tetraphenylpropne (38 mg, 7373, shown to be identical with an authentic sample synthesized by the method of Zimmerman et a1. 16…”

Steric and electronic effects on the photochemical reactivity of oxime acetates of β,γ-unsaturated aldehydes

“…The conclusion that the dimethyl-substituted radical is more stable than the dicyclohexyl-substituted radical is substantiated by bond dissociation data.14 All the evidence gathered regarding the effects of substitution on the outcome of the aza-di-n-methane from this study point to the fact that those dienes which fail to undergo the rearrangement do so because of a poorly stable cyclopropyl biradical. Further support for this concept of radical stabilization comes from our report of the successful synthesis of the triene 17 and its efficient photochemical cyclization to the corresponding cyclopropane 18.' The idea that deactivation was due to a free-rotor effect cannot be sustained.…”

“…92-94 "C (from hexane)] 4-(1,3-dithian-2-yl)-2,4-dimethylpent-2-enonitrile. Deprotection, oximation, and acetylation of the E-isomer afforded diene 3b (550 mg, 72%) as an oil; v,,,/cm-' 1710 and 1620; GH(CDC13) 7.7 (1 H, s, CH=N), 6.4 (1 H,s,vinyl H),2.1 (3 H,s,MeCO),1.9 (3 H,s,MeC=C) and 1 .4 (6 H,s,Me) ;G,(CDCl,) 168.3 (C=O),162.3 (C=N),150.4 (C=C),120.25 (C=C),112.6 (CN),39.6 (C),25.7 (Me),19.5 (MeCO) and 16.2 (MeC=C); A,,,/nm 229 (1600); m/z 179 (M' -15, 1%), 152 (loo), 135 (12), 122 (26), 119 (25), 107 (19), 92 (12) and 70 (12) (17), 181 (16), 139 (14), 124(38), 112(72),96(18), 79 (16) The desired butenal 11 (1 g, 84%) was obtained as an oil, which was used in the following step without further purification v,,,/cm-' 28 10,…”