Grignard reagents quinones

It is of interest to note that attachment of a basic side chain on carbon of an isomeric dibenzazepine affords a compound in which anticholinergic activity predominates, elantrine (50). Reaction of anthra-quinone (45) with the Grignard reagent from 3-chloro-N,N-dimethylaminopropane in THF in the cold results in addition to but one of the carbonyl groups to yield hydroxyketone 46. This is then converted to oxime 47 in a straightforward manner. Treatment of that intermediate with a mixture of phosphoric and polyphosphoric acids results in net dehydration of... 

The intramolecular oxidative cyclization of the anilinobenzoquinone 940 with a catalytic amount of palladium(II) acetate in the presence of copper(II) acetate in air afforded the carbazole-l,4-quinone 941 in almost quantitative yield. The regioselective introduction of the heptyl side chain at C-1 of the carbazole-l,4-quinone 941 was achieved by a 1,2-addition of the corresponding Grignard reagent to give the carbazole-l,4-quinol 942 in 55% yield. However, 1,4-addition at C-3 and 1,2-addition at C-4 led to the regioisomeric products 943 and 944 as well. Finally, under acidic reaction conditions, the carbazole-l,4-quinol 942 was smoothly transformed to... 

Reaction of organometallics such as alkyllithiums or Grignard reagents with p-quinones can give an addition product, or a hydroquinone (i.e. reduction product). The... 

A concerted electron transfer mechanism, with formation of an alkyl radical and quinone radical anion, has been proposed to account for the products of reaction of benzophenone with alkyllithium or Grignard reagents 92 the ratio of addition to reduction products is dependent on the alkyl group and not on the metal. 

Quinols. Alkyllithium reagents react selectively at the more electrophilic carbonyl carbon of unsymmetrical quinones. In contrast, Grignard reagents react selectively with the less hindered carbonyl group. 

Addition to quinone monoketals and quinol ethers.2 Complexation of quinone monoketals or quinol ethers with MAD permits 1,4-addition of organo-lithium and Grignard reagents. Highest yields obtain with aryl, vinyl, and acetylenic organometallics. 

Conjugate addition to quinone monoacetals.2 These substrates undergo only 1,2-addition with (CH3)2CuLi and most Grignard reagents, but 1,4-addition can be achieved by complexation of the acetal with 2 equiv. of 1. 

The one-pot reaction of 0-BOC protected salicylaldehydes and salicyl alcohols with electron-rich alkenes and a Grignard reagent involves a diastereoselective cycloaddition to an o-quinone methide and offers access to a wide range of 4-substituted chromans <02JOC6911>. 

Complexation of quinone monoketals and quinol ethers with MAD, followed by addition of organolithium or Grignard reagents gives products from 1,4-addition (Scheme 6.96) [120]. The success of these 1,4-additions is in marked contrast to re-... 

The first example of the enantioselective cycloaddition of chiral enol ethers to o-quinone methides, derived from a protected salicylaldehyde by reaction with a Grignard reagent, generates three chiral centres in a one-pot process and provides chiral chromans 30. These products can be manipulated to give other chiral chromans and chromenes and are a source of chiral aliphatic benzylic carbon sites <04JOC9196, 04SL1101>. 

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