Photochemische Reaktionen 130. Mitteilung. Zur Photochemie von 5,6‐Epoxy‐1,3‐dienen: Der Einfluss eines 7‐Hydroxysubstituenten auf die Carbenbildung

Abstract

Photochemistry of 5,6-Epoxy-1,3-dienes: Influence of a 7-Hydroxy Substituent on the Carbene Formation Summury On singlet excitation (A = 254 nm) in MeCN the hydroxy-epoxydiene (E)-4 undergoes photocleavage to the carbene intermediates d and e as main processes. The carbene d, showing behaviour typical of vinyl carbenes, undergoes addition to the adjacent double bond furnishing the cyclopropenes 5A + B. The carbene e, however, undergoes an insertion reaction into the neighbouring carbinol C, H-bond leading to the enol intermediate 21, which gives rise to the compounds 6A + B and 7A + B. To a lesser extent the products 8 A + B are formed via another enol intermediate (32). On photolysis of (E)-4 in MeOH instead of MeCN the enol intermediates 21 and 32 undergo rapid tautomerisation to the ketones 9A + B (main products) and 11.

Photochemical reactions. 143rd communication. Photochemistry of 5,6‐epoxy‐1,3‐dienes in the ionone series. Influence of a hydroxy group in the 7‐position

“…Reaction of 10 with MeLi afforded the alcohol 11 (92 YO), which was subsequently epoxidized by the method of Sharpless et al [5] leading stereoselectively to the epoxydiene (E)-5 (85 YO) with cis-relation of the OH with the epoxy function. [2] [6]. Therefore, only the most relevant spectral data of the new types of products are discussed here together with the chemical transformations which confirmed the assigned structures.…”

Carotenoids and polyterpenoids

“…In a synthesis of the 10-14-sulphur-bridged analogue (221) of retinal, the key step was the cyclizationsulphidation of (222) with thiourea in dimethylformamide at 230 "C, affording the thiopyranone (223).' l o The various acyclic analogues ( 224)-( 226) of retinal have been synthesized,' I ' as have the shorter analogues ( 227)-( 231), lacking the six-membered ring and differing in the length of the conjugated polyene chain.…”

Photochemical reactions. 144th Communication. Photochemistry of 5,6‐epoxy‐1,3‐dienes in the ionone series: Influence of a methoxy group in position 7

“…Evidence for the alternative carbene intermediate g is provided by the isolation of 15 (Scheme 3) which may be formed by carbene insertion into the adjacent C(7)-H bond in g3). However, the low yield (1 %) of 15 was surprising, since on photolysis of (E)-1, secondary products of the postulated enol corresponding to 15 were obtained in more than 30% combined yield [6]. On the other hand, on photolysis of (E)-5, compounds 14, (E)-16,17A + B, and 18 were isolated in yields similar to the corresponding hydroxy compounds on singlet excitation of (E)-1.…”

“…Bicyclo [3.2.O]heptyl Methyl Ketones 12 and 13 (Scheme 4). The structures and, in particular, the relative configuration at C (6) and C(7) of 12 and 13 was assigned by correlation with the alcohols 26 and 27 [2]. Thus, catalytic hydrogenation (Pd/BaS04) of 26 gave the double-bond isomer of the starting material (28) and, in addition, the two reduced diastereomeric products 29A and 29B6), presumably epimers at C (7).…”

“…When the chromatography of the photolysis mixture was not carried out in the presence of Et3N, instead of the enol ether 15, its hydrolysis product 19 [6], was isolated. 'H-NMR (300 MHz) analysis of the photolysis mixture showed a similar product distribution.…”