Photochemical acyl migration

Rearrangements arising by photochemically induced 1,3-acyl migrations have been reported in the 3tf-azepine239,181 and in certain l,3-dihydro-2JT-... 

The bc portion (267) was synthesized (Scheme 19) by treatment of the ethyl ester of i3, 3-dimethyllevulinic acid with hot ethanolic ammonia, followed by pyrolysis to give (275). Meanwhile, treatment of /8, 8-dimethyllevulinic acid with thionyl chloride gave the butyrolac-tone (276), and the sodium salt of this was treated with (275) to give (277). Photochemically induced acyl migration gave (278), which was treated with methanolic ammonia subsequent dehydration afforded (279), which was then activated by O- ethylation with Meerwein s salt to give (267). 

Isomerizations occurring from the appropriate vibrational levels of the singlet state could be concerted reactions involving a photochemically allowed, suprafacial 1,3-acyl migration with a transition state as represented by E below. Alternatively, homolysis could lead to a shfart-lived singlet biradical F which could rebond either... 

Berti, C. Gazz. Chim. Ital. 90, 559 (1960) photochemical example with acyl migration Tortajada, J., van Hemelrych, B., Morizur, J. P. Tetrahedron 40, 613 (1984)... 

Acetoxy)ethenylcarbene complexes of chromium underwent photochemically induced acyl migration to give ( )-but-2-ene-l,4-diones as the major product. ... 

The photochemical 1,3-acyl migration which converts certain jSy-unsaturated ketones into isomeric enones has been investigated for a series of compounds, including cholest-4-en-7-one (651) and its 6,6-dimethyl derivative (652). Photoequilibration affords the isomers (653), considered to arise via n — tt triplet states. The reactions are influenced by conformational and conjugative features which effect the stability of an intermediate radical pair of the type (654). Other workers have studied the phosphorescence spectra and lifetimes of triplet excited states of a number of j y-unsaturated ketones, including some... 

Uyehara, T, Furuta, T, Kabawawa, Y, Yamada, (., Kato, T., and Yamamoto, Y. (1988) Rearrangement approaches to cyclic skeletons. 6. Total synthesis of ( )-ptilocaulin on the basis of formal bridgehead substitution and photochemical [1,3] acyl migration of a bicydo [3.2.2]non-6-en-2-one system. J. Org. Chem., 53, 3669-3673. 

Photochemical reactions of a number of spirocylic compounds, such as 96, 97, and 98 (Scheme 22), upon triplet excitation have been investigated. - The direct excitation of ketones of type 96 led to an electrocyclic reaction and a-cleavage instead of 1,3-acyl migration. ... 

Photochemical reaction of complex tricyclic compounds 161, 162, 167, 168, and their congeners containing a P,y-enone chromophore follow a similar course on direct excitation. Thus, irradiation of 161 in ether leads to 1,3-acyl migration to give 163, which subsequently undergoes decarbonylation to yield the cyclopropyl compoimd 164. Interestingly, the ene-dione 162 underwent selective photoreaction characteristic of P,y-enones and furnished 165 and 166 on direct excitation in ether as a result of 1,3-shift followed by decarbonylation (Scheme 41). The tricycKc compounds 167,168, and their derivatives were also found to behave similarily. ... 

Suginome, H., Takemura, M., Shimoyama, N., and Orito, K., Photoinduced molecular transformations. 126. Photo double ring contraction of a 4a-homo-5a-cholest-3-en-l-one, a steroidal P,y-unsaturated cyclic ketone, involving photochemical 1,3-acyl migration,/. Chem. Soc., Perkin Trans. 1,2721, 1991. 

Uyehara, T., Kabasawa, Y., Furuta, X, and Kato, T., Rearrangement approaches to cyclic skeletons. III. Practical route to ds-bicyclo[4.3.0]non-4-en-7-onesbased on photochemical [l,3]-acyl migration of bicyclo[3.2.2]non-6-en-2-ones, Bm//. Chem. Soc. Jpn., 59, 539,1986. 

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