The reaction of o-lithiated O-aryl N,N-diethylcarbamates with (hetero)aromatic nitriles gives rise to functionalized salicylidene urea derivatives in high yields through a new 1,5-O → N carbamoyl migration. This Snieckus-Fries-type rearrangement nicely complements previously known O → C and O → O related shifts. In addition, when dimethylmalononitrile is used as the electrophilic partner, the carbamoyl shift is preferred over the expected transnitrilation reaction.

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ABSTRACT:The use of t-BuLi at low temperature selectively leads to -lithiation of benzyl phenyl ether generating a stable organolithium, which can be efficiently trapped with a variety of selected electrophiles prior to suffering the expected [1,2]-Wittig rearrangement. In the case of (o-alkynyl)phenyl benzyl ethers, the intermediate -aryloxyorganolithium undergoes an unexpected anti intramolecular carbolithiation reaction leading to functionalized benzo[b]furan derivatives.

The -lithiobenzyloxy group, easily generated from aryl benzyl ethers by selective -lithiation with t-BuLi at low temperature, behaves as a directed metalation group (DMG) providing a straight access to o-lithiophenyl -lithiobenzyl ethers. This ortho-directing effect is reinforced in substrates bearing an additional methoxy group at the meta position. The generated dianions can be reacted with a selection of electrophiles including carboxylic esters and dihalosilanes or germanes, which afford interesting benzofuran, sila(germa)dihydrobenzofuran and silachroman derivatives from simple aryl benzyl ethers.

The reactions of o-lithiated O-aryl N,N-diethylcarbamates with different CN multiple bond electrophiles have been thoroughly studied. A 1,5-O→N carbamoyl shift, a new variation of the anionic Fries-type rearrangement, takes place when nitriles, imines or alkylcarbodiimides are employed. In these cases, the carbamoyl group plays a dual role as directing group and building up a variety of functional groups through the 1,5-O→N carbamoyl migration. On the other hand, the use of iso(thio)cyanates and arylcarbodiimides led to non-rearranged o-functionalized O-arylcarbamates.This reactivity was further computationally explored, and the governing factor could be traced back to the relative basicity of the alternative products (migrated vs non-migrated substrates). This exploration also provided interesting insight about the degree of complexation of the lithium cation onto these substrates. A new access to useful 2-hydroxybenzophenone derivatives has also been developed.