2,5-cyclohexadienone monoacetals

I 7 Copper-catalyzed Enantioselective Conjugate Addition Reactions of Organozinc Reagents Tab. 7.4. Conjugate additions to 2,5-cyclohexadienone monoacetals and ethers. 

Scheme 7.18. Selective cis or trans double conjugate addition of Et2Zn to cyclohexadienone monoacetal 66.

Thallium trinitrate oxidi2es naphthols and hydroquinone monoethers, respectively, to quinones and 4,4-diaIkoxycyclohexa-2,5-dienones, eg, 4,4-dimethoxy-2-methyl-2,5-cyclohexadienone [57197-11 -2] (108) (111,112). The yield of (108) is 89%. Because the monoacetal is easily converted to the quinone, the yield of 5-hydroxy-l,4-naphthoquinone [481-39-0] is 64%. 

A more detailed study of this process has sought to establish the scope of the process. Thus Schultz and his coworkers have reported that irradiation of the cyclohexadienone (269) affords the adduct (270). This process can be quantitative using extended photolysis times but if the reaction is stopped after 14 h a 1 1 mixture of (270) and (271) is obtained. Other examples of the process are reported. The irradiation of a series of quinone monoacetals (272) in acetic acid has provided a flexible high yield route to substituted cyclopentenones. Such a rearrangement path is typical of the processes encountered in the photochemical rearrangement of cross conjugated cyclohexadienones. Some examples of the utility of this system are shown in Scheme 9. - ... 

The migration of oxygen from a quaternary center in a cyclohexadienone may be preferred to a carbon shift, when present as an ether or ester function rather than free hydroxy. Thus the p-quinol acetate (117) yields the orcinol monoacetate (118 79%) on treatment at room temperature with trifluoroacetic anhydride, and the p-quinol ether (119) forms the resorcinol diethyl ether (120 71%) in ethanolic sulfuric acid. In the second case, hemiketalization must intervene also some methyl shift (12%) is observed. With the quinol (121), treatment with acetic anhydride-sulfuric acid leads to the lactone (122) acetylation or lactonization probably precedes oxygen shift. A number of related examples can be found in the steroid area. - Thermal 1,3-shifts of p-quinol acetates can also be induced acetate (117) yields catechol acetate (123 50-60%, 45 °C) by way of isomerization of the first-formed acetate (124). In the o-quinol acetate series, 1,2-acetoxy shift is seen in (125) (126 92%) and in (127) (128 90%), both in... 

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