Photochemical addition alcohols

Alcohols add to olefins upon irradiation in two modes, to produce higher alcohols and to produce ethers. In most photochemical additions of alcohols the first mode occurs ... 

Additions to Aromatic Hydrocarbons. A variety of photochemical additions to aromatic hydrocarbons have been reported. Benzene and its derivatives add to maleic anhydride74-76 as well as to simple olefins,77-80 isoprene,81 acetylene derivatives,79,82 and alcohols.83 The mechanism of the maleic anhydride-benzene reaction is discussed in Section IV. A.4. Naphthalene forms a photoadduct with dimethyl acetylenedicarboxylate62 and with acrylonitrile8211 while anthracene behaves similarly with maleic anhydride84 and with 1,2-benzanthracene.85 The photoaddition of several aromatic amines to anthracene has been reported to proceed via a charge transfer complex86,87 in fact, the majority of these addition reactions may proceed in this manner. 

It is pertinent to mention the formation of y-ketols by photochemical addition of alcohols to enones follows the same polarity pattern [193],... 

In addition reactions an excited, unsaturated molecule uses its weakened rr bond to form two new o bonds when these a bonds form a new ring in the molecule MN the reaction is one of cycloaddition . Thus alkenes can add photochemically to alcohols, as shown in Figure 4.51(a) to form a non-cyclic adduct or to other alkenes in cycloaddition processes Figure 4.51(b). 

Scheme 52 provides a sample of the types of reactions that have recently been conducted under a variety of different conditions. Example (1) illustrates the classical conditions,163 while example (2) shows that modified initiators that permit low temperature reactions may prove beneficial.29 Finally, example (3) illustrates that the photochemical addition of alcohols (and also acetals) to enones in the presence of benzophenone is a very useful preparative procedure.164 Here, the carbinyl hydrogen is abstracted by an excited state benzophenone molecule rather than a peroxy radical.163... 

On the other hand, photochemical addition of alcohols to conjugated dienes, observed in the case of cholestadieiie-3,5, is probably related to the reactions observed when vitamin A acetate is irradiated in methyl alcohol. It is also possible that the photoisomerization of acyclic trienes to allenes is related to the as yet incompletely studied dimerization reactions of larger polyenes. 

Example 5.4. Photochemical addition of trifluoroiodomethane to allyl alcohol. 

Photochemical addition of alcohols and acetic acid to the enone double bond of Decompostin (123) affords the adducts (124) in high yield when the irradiations are carried out in benzene solution. Dimethyl acetylenedicarboxylate photoadds to the pyrone (125) under sensitized conditions to yield the benzene derivative (126) presumably by decarboxylation of the (4-l-2)-adduct (127). Adducts of this type (128) are obtained by the sensitized addition of acrylonitrile to the same substrate. The (2+2)-adduct (129) is formed also but in low yield. ... 

The xylene-sensitized photochemical addition of hydroxylic compounds (water or alcohols) to limonene has been described in further detail by Kropp. A 1.2 1 mixture of cis- and tra s-) -terpineol (142a,b R = H) is obtained on irradiation of an aqueous solution containing a trace of xylene, or the corresponding methyl ethers (142a, b R = Me) when methanol is the solvent. A trace of mentha-l(7),8-diene (143) and extensively racemised limonene is also found, supporting the idea that the reaction goes through the symmetrical carbonium ion (141). 3... 

Dihydropyrimido[4,5-t/]pyridazines 1 (accessible by the reaction of pyrimido[4,5-z/]-pyridazines with organometallic compounds62 or by the photochemical addition of alcohols 63 see Section 7.4.6.2.) are oxidized to the fully conjugated pyrimido[4,5-<7]pyndazine system 2 by 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) or potassium hexacyanoferrate(III).61... 

Photochemical addition of alcohols or ethers also leads to 4-substituted 5,8-dimorpholino-2-phenyl-3,4-dihydropyrimido[4,5-i/]pyridazines, e.g. 6.63... 

Marshall, J.A. Carroll, R.D. The photochemically initiated addition of alcohols to 1-methene. Anew type of photochemical addition to olefins. J. Am. Chem. Soc. 1966,88, 4092—4093. 

Hibaone has been synthesized using the photochemical addition of A -podo-carpen-13-one to ethylene or 1,2-dichloroethylene. Treatment of the adduct (309) with methyl-lithium, and acetolysis of the resulting tertiary alcohol (310), gives an acetate (311) which is readily converted into hibaone. 

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