Isocyanides, acid catalyzed

Formamides can be prepared by the acid-catalyzed addition of water to isocyanides. The mechanism is probably ... 

Various a-addition reactions are observed to be metal- or acid-catalyzed, or to be uncatalyzed. In this review only the metal-catalyzed reactions will be discussed, since it is generally assumed that metal isocyanide complexes are involved in these systems. A number of metal-catalyzed a-addition reactions have been mentioned recently. Copper(I) oxide seems to be the most commonly used catalyst, although other metal complexes sometimes are satisfactory. Table III presents a partial survey of this work. 

Almost accidentally, Bienayme and Bouzid discovered that heterocyclic amidines 9-76 as 2-amino-pyridines and 2-amino-pyrimidines can participate in an acid-catalyzed three-component reachon with aldehydes and isocyanides, providing 3-amino-imidazo[l,2-a]pyridines as well as the corresponding pyrimidines and related compounds 9-78 (Scheme 9.15) [55]. In this reachon, electron-rich or -poor (hetero)aromatic and even sterically hindered aliphatic aldehydes can be used with good results. A reasonable rahonale for the formation of 9-78 involves a non-con-certed [4+1] cycloaddition between the isocyanide and the intermediate iminium ion 9-77, followed by a [1,3] hydride shift. 

The acid-catalyzed reaction of oxetanes with t- butyl isocyanide gives 2-iminotetra-hydrofurans, boron trifluoride etherate being used as catalyst (equation 26). The authors proposed that the isocyanide reacts with the protonated oxetanes by an N2 mechanism (70S475). 

Isocyano-l-tosylcyclobutane (20) can be prepared in 71 % yield by intermolecular cyclodialkylation of tosylmethyl isocyanide with 1,3-dibromopropane in the presence of sodium hydride.12 Cyclobutane 20 can also serve as an appropriate precursor of cyclobutanone indeed, smooth acid-catalyzed hydrolysis provides cyclobutanone in 84-88% yield.29... 

Cleavage of oxetanes.2 In the presence of Znl2, oxetanes are opened by cyanotrimethylsilane regioselectively to y-hydroxy isocyanides, which undergo acid-catalyzed hydrolysis to y-amino alcohols. 

Complexes containing unusual isocyanide ligands have evolved from attempts to alkylate the anions [M(CN)6]4 (M = Fe, Ru, Os) with [Et3OJBF4 in acetone solution. The compounds isolated [M CNCMe2 CH2COMe)6](BF4)2 resulted from an initial acid-catalyzed aldol condensation of the acetone solvent followed by a nucleophilic attack of the carbon-... 

This review focuses on the transition metal mediated polymerization of isocyanides and 1,2-diisocyanobenzenes. Other approaches, including acid-catalyzed polymerization and main-group metal mediated polymerization, are also included, but only if they are closely related to the above topic. 

Additionally, for catalyzed reactions, an example for synthesis of tetrazoles by reacting isonitriles and azides was reported. Yamamoto et aL reported that the acid-catalyzed [3-1-2] cycloaddition between isocyanides 322 and trimethylsUyl azide (146) in the presence of methanol gives the desired 1-substituted tetrazoles 323 in good yields (Scheme 68) [ 177-179). 

The chemistry described by Saegusa, Kobayashi, and others (Sehemes 1 to 4 and Table 1) is reminiscent of the earlier work by Zeeh (Scheme 5) [16-18]. These Lewis acid-catalyzed reactions of isocyanides with ketones are shown in equation 3. The A/-/crt-butyl group in 37 is removable by boron trifluoride etherate. A suggested pathway is illusttated in equation 3 and is initiated by BE3 activation of the aryl ketone (38). Some indoles prepared by Zeeh are 39-41 [17]. The elegant free-radical cyclization of aryl isocyanides developed by Fukuyama is presented in Chapter 49. 

The acid-catalyzed cyclization of P-keto isocyanides to oxazoles has previously been reported in Hagedom, 1. Etling, H. Angew. Chem. 1961, 73,26-27. 

Synthesis of a-hydroxycarbo mides by acid catalyzed reaction of an isocyanide with an aldehyde or ketone (see 1st edition)... 

Acid-catalyzed iminium ion 57 fonnation is followed by isocyanide 54 addition and capture of the remaining nitrilium ion 58 by the carboxylate of 56 to generate compound 59. A rapid O N acyl transfer takes then place in order to obtain dipeptide 60 as a mixture of epimers at C4. Although the control of the stereochanistry of the newly formed stereocenter still remains a problan of the Ugi reaction, it nicely demonstrates the force of the Ugi MCR, as all of the carbon atoms needed are successively assanbled in a single step [22], Mannich-type 4CR are often used for the synthesis of natural products. One example is the synthesis of the alkaloid ( )-roelactamine 65 (Scheme 6.6). The reaction of piperonal 61 with methylamine, Grignard reagent 62, and acid chloride 63 results in the formation of amide 64, which... 

T. Yue, M.-X. Wang, D.-X. Wang, G. Masson, J. Zhu, Angew. Chem. Int. Ed. 2009,48, 6717-6721. Brpnsted acid catalyzed enantioselective three-component reaction involving the a-addition of isocyanides to imines. 

More recently, Zhu and coworkers reported an efficient chiral Lewis acid-catalyzed Passerini SCR rendering final adducts in good to excellent enantioselectivities for a variety of nonchelating aldehydes, carboxylic acids, and isocyanides as represented in Figure 8.3 [38]. 

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