1.4- Benzoquinones stereospecific reactions

Olefinic double bonds substituted with one or more electron-withdrawing groups show significant dipolarophilic activity in cycloaddition reactions with organic azides,43,276-278 similar to the electron-rich double bonds of enamines and enol ethers the reactivity is less pronounced in azide additions compared to that observed in diazomethane reactions.7 The first triazolines reported resulted by the action of aryl azides on benzoquinones.1,279-281 As a rule, stereospecific cis additions occur,32 which are usually unidirectional except in the case of methacrylic derivatives67 and certain alkenes bearing... 

Reactions with quinones, anthraquinone synthesis. Early studies of McElvain indicated that the reagent reacts in two different ways with quinones. In the case of benzoquinones the products are 1 1 adducts, which are ethoxyfurane derivatives. 2-Halonaphthoquinones were found to react at least in part with 2 equiv. of 1 to form 1,3-diethoxyanthraquinones (with loss of the halogen substituent). A more recent study established that the reaction of halonaphthazarins with 1 is stereospecific, i.e., only one anthraquinone is formed under suitable conditions yield of 1 2 adducts can be as high as 60 /o. A typical reaction is formulated in equation (I). The 1 1 adducts are major products, however, in the absence of a free peri-hydroxyl group. ... 

The photochemical addition of 9,10-phenanthraquinone, tetrachloro-1,2-benzoquinone (and benzil) to alkenynes (285) has been reported.167 The addition of the quinones takes place to the ethylenic bond of the alkenyne to yield alkynyl dioxins (286) and (287). The reaction is not stereospecific and a biradical intermediate is proposed to account for the loss of the stereochemical integrity of the olefin. Ishibe et a/.168 have published the results of an investigation of the photoaddition of p-benzoquinone, 1,4-naphthoquinone, 2-methyl-1,4-benzoquinone,... 

---