Diazomethane, reaction with benzoquinones

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... 

The Diels-Alder cycloaddition reaction of 2,6-dimethyl-1,4-benzoquinone with methyl (ii)-3,5-hexadienoate, carried out in toluene as solvent, gives only traces of the cycloadduct shown in Eq. (5-160), even after seven days. However, when the solvent is changed to water and sodium ( )-3,5-hexadienoate is used as the diene, 77 cmol/mol of the desired cycloadduct is obtained after one hour and esterification with diazomethane [714] f Again, hydrophobic interactions between diene and dienophile in the aqueous medium seem to be responsible for this remarkable and synthetically useful rate acceleration. 

P NMR was used to examine the products from the reaction of both 1 2 and 1 4 benzoquinones with trimethylphosphite (Argy-ropoulos and Zhang 1998). The former formed cyclic trimeth-ylphosphate derivatives of the hydroquinones in a reaction comparable to that with diazomethane, and were hydrolyzed to 2-hydroxyphenyldimethylphosphates. The 1 4 quinone formed 1-methoxy-4-phenyldimethyl phosphate. 

A kinetic study of reactions of 2,3-dichloro-5,6-dicyano-pflra-benzoquinone (140, DDQ) with silyl enol ethers, silyl ketene acetals, allylsilanes, enamino esters and diazomethanes has been carried out in acetonitrile and DCM, allowing correlations with nucleophilicity parameters for the latter species to be examined. These are found to be 2-5 orders of magnitude larger than expected for Single Electron Transfer processes, supporting a polar mechanism for C-C bond formation at C(5). However, rate constants for (9-attack do correlate well with calculated values assuming rate-determining SET. 

Eistert, B. and Bock, G., Reactions of a-dicarbonyl compounds and quinones with diazoalkanes. II. The reaction of some substituted p-benzoquinones with diazomethane to p-epoxymethylcyclo-... 

---