Reactions of o-xylylenes produced photochemically from o-alkylstyrenes

Abstract

The potential synthetic utility of o-xylylenes generated photochemically from o-alkylstyrenes has been investigated. The o-xylylenes produced from 3a, 3b, and 3c were trapped with cyclohexene to yield octahydroanthracene derivatives in good yields (94,86, and 63%, respectively). In the absence of cyclohexene, the o-xylylene from 3a dimerized to produce 8. Irradiation of 16 gave an o-xylylene which is an enol and which subsequently tautomerized to aldehyde 9. Deuterium-labeling studies supported this mechanism. The quantum yield for formation of 9 upon direct irradiation of 16 was 0.085, and that for the xanthone photosensitized process was 0.027.Thermal and photochemical reactions of sodium salts of P-phosphono tosylhydrazones have been investigated. When the sodium salt of dimethyl a-acetylmethylphosphonate tosylhydrazone is heated, the dimethoxyphosphonyl anior , though a relatively strong base, was eliminated. On the other hand, ultraviolet irradiation of the sodium salts of P-phosphono tosylhydrazones leads to dimethoxyphosphonyl-substituted olefins, presumably via the carbene intermediate. Some of the products result from a previously unreported phosphonyl group migration to a carbene.The migration of phosphonyl groups t o electron-deficient centers has been intensively investigated for carbonium o x y g e r~,~ a n d n i t r~g e n .~ In t h e migration

Visible light-mediated hydrogen atom transfer and proton transfer for the conversion of (2-vinylaryl)methanol derivatives to aryl aldehydes or aryl ketones

“…12,13 For example, the conversion of (2-(1-phenylvinyl)phenyl)methanol to the corresponding 2-(1-phenylethyl)benzaldehyde under UV irradiation was reported by Hornback's group in 1979 (Scheme 1a). 14 As shown in Scheme 1a, it must be emphasized here that due to the harsh UV irradiation, the photochemical reaction product was only obtained in 6.3% yield in the absence of a photosensitizer, and even with the addition of xanthone as a photosensitizer, the corresponding benzaldehyde was obtained only in 15.1% yield. The low yield is probably due to the Norrish-type reaction 15 of 2-(1-phenylethyl)benzaldehyde under UV light irradiation, which leads to the decomposition of the obtained product.…”