Acetic from photolysis

Herz and Iyer have proposed an a-cleavage mechanism with the intermediacy of a cyclopropyl ketene for formation of the polycyclic acetal 42 from photolysis of the rigid cyclopentenone 4339 The cleavage reaction is thought to occur via an n,7r triplet state of unusually high energy for a cyclopentenone (75 kcal/mole). 

Naphthyl(methoxycarbonyl)carbene (29) has been investigated in low temperature matrices, and in flash-photolysis experiments. " In each of these complementary studies the carbene was generated from the a-diazo ester, methyl 2-diazo-(2-naphthyl)acetate. Matrix photolysis of the precursor at 450 nm yields primarily the triplet ground-state carbene, which has been... 

Figure 4.4>5 Ratio of products produced from photolysis of a-naphthyl acetate in CO2 (data taken from Reference 56).

Lewis acids efficiently catalyze the transfer of diazoketones and diazoesters to amides and nitriles to furnish 2,4,5-trisubstimted oxazoles (Scheme 1.49). In particular, Eguchi and co-workers found that BF3 OEt2 was the best catalyst for reaction of the adamantyl diazoketoester 180 with acetonitrile. Attempts to prepare 181 using Rh(II)acetate or photolysis were unsuccessful. Similarly, Ibata and Isogami °° described a general synthesis of 5-aryl-2-(chloromethyl)oxazoles 183 from a BF3.0Et2-catalyzed addition of a-diazoacetophenones 182 with chloro-acetonitrile. The yields were quite respectable (Table 1.12). 

From Diazo-compounds. The Wolff rearrangement of a-diazo-ketones has been reviewed and a discussion of the Bamford-Stevens reaction and its associated mechanisms has appeared. The details of a cryochemical synthesis of cyclo-propanone from keten and diazomethane have been described, as have syntheses of cyclopropanone and cyclopropanone acetal. The photolysis of 1-diazobutane, resulting in methylcyclopropane, has been subjected to physico-chemical study. 

G., Photoreactivity of some a-arylvinyl bromides in acetic acid. Selectivity toward bromide versus acetate ions as a mechanistic probe, J. Am. Chem. Soc., 113,4261,1991. See also (b) Kitamura, X, Kabashima, X, Kobayashi, S., and Taniguchi, H., Isolation and alcoholysis of an ipso adduct, vinylidenecyclohexadiene, from photolysis of l-(p-ethoxyphenyl)vinyl bromide. Tetrahedron Lett., 29, 6141, 1988 (c) Kitamura, X, Nakamura, I., Kabashima, X, Kobayashi, S., and Taniguchi, H., A novel spiro adduct from intramolecular ipso substitution in the photolysis of an a-[p-(2-hydroxyalkoxyjphenyl]vinyl bromide,/. Chem. Soc., Chem. Commun., 1154, 1989 (d) Kitamura, X, Kobayashi, S., and Xaniguchi, H., Photolysis of vinyl halides. Reaction of photogenerated vinyl cations with cyanate and thiocyanate ions,/. Org. Chem., 55, 1801, 1990 (e) Hori, K., Kamada,... 

The 2-nitrobenzylidene acetal has been used to protect carbohydrates. It can be cleaved by photolysis (45 min, MeOH CF3CO3H, CH2CI2, 0°, 95% yield) to form primarily axial 2-nitrobenzoates from diols containing at least one axial alcohol. ... 

Dipolar cycloadditkm reactions of nitrones to olefins, 46, 1,3-Dipolar cycloadditions with 3-phenylsydnone, 45, 98 Dispiro[5 1 5 l]tetradecane-7,14-dione, photolysis to cyclohexylidene-cyclohexane, 47, 34 preparation from cyclohexanecarbonyl chlonde and triethylamine, 47,34 Displacement of bromine from 1-bromo-2-fluoroheptane to give 2-fluoro-heptyl acetate, 46, 37... 

Nitro 2-nitrosO N-rnethylaniline, green prisms from acet/w, mp 165—67° with decompn prepd by the photolysis of N-(2,4-dlnitrophenyl)-N-methyl-leucine (Ref 9)... 

Arylthallium bis(trifluoroacetates) (see 12-21) can be converted to aryl nitriles by treatment with copper(I) cyanide in acetonitrile. Another procedure uses excess aqueous KCN followed by photolysis of the resulting complex ion ArTl(CN)3 in the presence of excess KCN. Alternatively, arylthallium acetates react with Cu(CN)2 or CuCN to give aryl nitriles. Yields from this procedure are variable, ranging from almost nothing to 90 or 100%. 

As stated previously, the photolysis of cyclobutanone in ethanol solution results in an 8% yield of an acetal, presumably formed from ethanol addition to a carbene intermediate. Alkylation of the a positions of cyclobutanone increases the yield of this rearrangement product,(22)... 

When 3-methoxybenzyl acetate is photolyzed, however, the products expected from free radical coupling are decreased and a substantial amount of 3-methoxybenzylalcohol results. A carbonium ion intermediate has been proposed in the photolysis of this meta ester ... 

The isolation of benzvalene (61) from the irradiation of benzene at 254 nm and the observation that this compound produces the expected bicyclic ethers when treated with acidified methanol lend credence to the intermediacy of (61).(90> Photolysis of benzene in acetic acid was found to result in formation of acetates (64)—(67), with the product composition changing with time ... 

Extrapolation of the data to zero time suggests that the endo acetates (65) and (67) are produced in amounts as great as or greater than the exo isomer. Solvolysis studies of the bicyclo[3.1.0]hex-2-en-6-yl cation reveal that nucleophilic capture occurs preferentially from the exo side to give (66) rather than (67). Similarly, solvolysis of cation (63) leads to exo product (64) in at least a 90% yield. Photolysis of benzene in deuteriophosphoric acid results in (68), in which all the deuterium is incorporated into the 6-endo position ... 

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