Dichlorodicyanoquinone

Several methoxy-substituted benzyl ethers have been prepared and used as protective groups. Their utility lies in the fact that they are more readily cleaved oxidatively than the unsubStituted benzyl ethers. The table below gives the relative rates of cleavage with dichlorodicyanoquinone (DDQ). ... 

Dichlorodicyanoquinone (DDQ), CH2CI2, H2O, 40 min, it, 84-93% yield.This method does not cleave simple benzyl ethers. This method was found effective in the presence of a boronate. The following groups are stable to these conditions ketones, epoxides, alkenes, acetonides, to-sylates, MOM ethers, THP ethers, acetates, benzyloxymethyl (BOM) ethers, and TBDMS ethers. 

Benzyl groups having 4-methoxy (PMB) or 3,5-dimethoxy (DMB) substituents can be removed oxidatively by dichlorodicyanoquinone (DDQ).181 These reactions presumably proceed through a benzylic cation and the methoxy substituent is necessary to facilitate the oxidation. 

The yellow crystalline azaberbinone (388) has been prepared by several, closely related methods. Dehydrogenation of betaine 378 (Section III,E,2) with dichlorodicyanoquinone gives compound 388 directly. Alternatively, this compound (388) has been prepared in three ways from 6 -nitropapaverine (385) (Scheme 15) (i) Treatment of compound 385 with triethyl phosphite gives a low yield of betaine 388 directly (ii) compound 385 in methanolic KOH at reflux temperature gives the anthranil 386 which rearranges to the betaine 388 in hot triethyl phosphite and (iii) iodine oxidation of 6 -nitro-papaverine (385) generates the A-oxide 387 which is reduced to the betaine 388 by sodium bisulfite. The chemistry of compound 388 remains unexplored. 

N-Methyl- and N-phenyl-2-vinylpyrroles 20a,b react with DMAD at reflux temperature in chloroform to give, in moderate yields, the dihydroindoles 22 via a 1,3-H shift from the Diels-Alder intermediate 21 (55-75%) (80JOC4515). These adducts were readily converted into the corresponding indoles 23 with Dichlorodicyanoquinone (DDQ). 2-Vinyl-pyrrole failed to give [4 + 2]-cycloadducts with acetylenic esters (80JOC4515). Spectroscopic analysis of the product mixtures indicated the presence of polymeric compounds resulting from Michael addition reactions. 

That the chalcone units combined in a head-to-tail manner was conclusively decided by showing that the thiolane could be dehydrogenated by dichlorodicyanoquinone in boiling chlorobenzene to a dibenzoyldiphenylthiophene, 8, whose 13C NMR revealed the presence of two different benzoyl groups (18). It followed that each of the two possible modes of head-to-nead fusion of chalcone units in a thiolane could be rejected. 

The mechanism of dehydrogenation of aromatic compounds with dichlorodicyanoquinone (DDQ) is shown in Scheme 7,32. 

Schiff bases (14), which are formed by reaction between DAMN and appropriate carbonyl reagents, are oxidatively cyclized to give a variety of 2-substituted 4,5-dicyanoimidazoles (15) (Scheme 2.1.5). Although dichlorodicyanoquinone (DDQ) or diaminosuccinonitrilc (DISN) have been used frequently to achieve the oxidative cyclization, long reaction times (17 h to 4 days under reflux) are a disadvantage, and N-chlorosuccinimide (NCS) under basic conditions is more convenient in many cases. The Schiff bases are best formed from aromatic aldehydes, but aliphatic aldehydes and ketones, ketoesters, orthoesters, amides, imidates and cyanogen chloride have all been used [15, 41-49J. 

The subsequent development of other synthetically useful routes to alkoxycyclopro-penes has provided ready access to the cyclopropenyl cations using trityl perchlorate or fluoroborate as hydride abstracting reagents Dichlorodicyanoquinone has also been used for this purpose ... 

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