Conjugated isonitriles

Conjugated isonitriles. Isocyanoalkyl epoxides undergo ring opening by reaction with LHMDS. The ( /Z)-isomer ratios are different from (usually higher than) those arising from using LDA. 

Polymeric (isocyanide)gold(i) aryls ( gold oligo-phenylene-ethynylene-isonitriles ) were tested as electrical conductors at metal-molecule-metal junctions (7r-conjugated molecular wires), but the preparation, structure, and properties of the materials were not fully disclosed (Scheme 52).218... 

Abstract Described are the synthetic routes to precisely defined molecular wires which are of discrete length and constitution. They are fully conjugated systems and are expected to have nearly linear current-voltage response curves. Their ends are functionalized with molecular alligator clips, based on chalconides and isonitriles, for adhesion between proximal probes. Both solution and solid-phase approaches have been used to prepare these molecular wires that are based on oligofthiophene ethynylene)s and oligofphe-nylene ethynylene)s. Molecular device syntheses are also described that would be expected to have nonlinear current-voltage responses. 

A similar cyclization can result from lithiation of an isonitrile lithiation of 553 requires two equivalents of LDA and the organolithium 554 can either be trapped with other electrophiles at low temperature or warmed to give an indole 555 (Scheme 219) . It is quite clear that isonitriles activate purely by conjugation, and indeed they promote deprotonation of methyl groups para to an isonitrile just as well as ortho. The ease with which isonitriles can be made from formamides suggests that these methods could be rather more widely used than they are. 

The first application of NMR diffusion measurements to determine the aggregation state of a transition metal catalyst concerned the chiral, tetranuclear Cu(i) catalysts 130-132, used in the conjugate addition reactions of anions to a,p-unsatu-rated cyclic ketones. Compounds 130-132 react wdth isonitriles to form 133-135, and do not degrade to lower molecular weight species (see Eq. (20)) [109]. 

The facile reduction of the intermediate carbonium ion again indicates a considerable donation of the iron d electron to the unoccupied p-orbital of the isonitrile carbon. The rapid rate of reduction seems also to argue for a transition state or intermediate such as shown in Equation 8, which yields a conjugated system through which the electrons can be transferred rapidly. 

Except for the well-documented conjugate additions of diethylaluminum cyanide,92 triethylaluminum-hydrogen cyanide and Lewis acid-tertiary alkyl isonitriles,93 examples of Lewis acid catalyzed conjugate additions of acyl anion equivalents are scant Notable examples are additions of copper aldimines (233),94, 94b prepared from (232), and silyl ketene acetals (234)940 to a,(3-enones which afford 1,4-ketoal-dehydes (235) and 2,5-diketo esters (236), respectively (Scheme 37). The acetal (234) is considered a glyoxylate ester anion equivalent. 

Reactions of arylazosulfones (52) with conjugate bases (53) and (54) of active-methylene isonitriles in DMSO give 1-arylimidazoles (55) and (56), respectively.50... 

Cyclopropyllithiums stabilised additionally by conjugating groups (alkynes20 or nitriles,21 22 -but not isonitriles, which maintain configurational stability23 - for example) do not retain their stereochemistry, even though they retain some pyramidal character. 

In tMs approach, conjugate addition of the anion from an isocyano-acetate to an a,p-unsaturated nitrocompound with evenmal loss of nitrous acid, produces 5-unsubstituted pyrrole-2-esters. The example below shows a mechanistic sequence that can be seen to parallel that in the van Leusen synthesis. The most useful route to the a,P-unsaturated nitro-compound involves the base-catalysed condensation of an aldehyde with a nitroalkane giving an a-hydroxy-nitroalkane it can alternatively be generated in situ, in the presence of the isonitrile, using diazabicycloundecane (DBU) as base on the 0-acetate of the a-hydroxy-nitroalkane (for an example see 16.16.2.1). The process works even when the unsaturated nitro unit is a component of a polycyclic aromatic compound. ... 

With cyanide as the nucleophile, 1,4-DCB yields 4-cyanophenylsubstituted cyanoalkanes from a variety of alkenes and dienes. Highest yields are obtained when the alkene or diene has an oxidation potential <1.5 V vj. SCE. Both nitriles and isonitriles are obtained from the alkenes studied whereas only nitriles were detected from conjugated dienes. With fluoride ion, 4-cyanophenylsubstituted fluoroalkanes were obtained from alkenes but not from conjugated dienes. 

In contrast to their terrestrial relatives, those isonitriles of marine origin are terpenoid based, rarely possess conjugated systems and are often accompanied by the corresponding isothiocyanates or formamido compounds, i.e. the triad RNC, RNCS, RNHCHO occurs (Figure 28). Several dozen such compounds are known, mostly from species of tropical sponges ... 

In organocopper compounds, an insertion reaction proceeds on carbon monoxide, isonitrile and carbon dioxide [58]. For example, carbon monoxide inserts into organocopper compounds to afford the ketone as shown in eq. (22.36) [89]. The 1,4-addition of organocopper compounds proceeds on the conjugate carbonyl compounds as shown in eq. (22.31), described above. On the other hand, a 1,2-addition proceeds stereospecifically on non-conjugated aldehydes or ketones [54,90]. 

This chemistry was extended to a catalytic conjugate addition of cyanide to cx-substituted cx,p-unsaturated fV-acylpyrroles 15 followed by enantioselective protonation (Scheme 13) [53]. In this reaction, gadolinium enolate was generated in situ via conjugate addition of a gadolinium isonitrile to 15. Products 16 containing cx-secondary alkyl- and a-aryl-substimted tertiary stereocenters, which are usually difficult to access via enantioselective alkylation or arylation, were successfully produced, in addition to a-methyl and ethyl-substituted A -acylpyrroles. 

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