Isonitriles from amides

Calcium carbonate a-Ketocarboxylic acid amides from isonitriles and carboxylic acid chlorides via a-ketiminochlorides... 

Synthesis of a-acylaminocarboxylic acid amides from isonitriles... 

The Ugi reaction produces a-amino acid amides from four components (isonitrile, carboxylic acid, aldehyde, and amine) in a one-pot reaction. With glycosylamines and ZnCl2 as promoting Lewis acid, a-amino acid amides are obtained [13,45] with excellent stereoselectivity in these reactions. For example, the galactosylamine 2 gave Ugi product 30 with formic acid as carboxylic component and various aldehydes and isonitriles in high yields and a diastereoselectivity of 19 1 in favor of the D-amino acid amides 30 (Scheme 20). 

Titanium tetrachloride (x-Alkoxycarboxylic acid amides from acetals and isonitriles... 

Without additional reagents N-Heterocyclic a-ketocarboxylic acid amides from o-formyl-N-oxides and isonitriles... 

Synthesis of a-acylaminocarboxylic acid amides, oligopeptides, and j -lactams from isonitriles s. 17, 809... 

Several examples of the monocyclic isothiocyano sesquiterpenoids having the bisabolane (83) skeleton are known. Along with the hydrocarbon theonellin (84), isothiocyanate 86 and formamide 87 were obtained from the Okinawan sponge Theonella cf. swinhoei. It seems remarkable, but not unusual, that not only was the amide the major constituent, but the isonitrile 85 was the missing member of the triad [57], Relative stereostructures were indicated by NMR analysis of theonellin formamide (87) and its transformation products. 

This procedure illustrates the best way to prepare aryl isocyanides. It is quite general, having been used by Ugi and Meyr e to make the following isocyanides from the corresponding form-amides phenyl (56%), />-tolyl (66%), 2,6-dimethylphenyl (88%), mesityl (80%), o-chlorophenyl (43%), -chlorophenyl (54%), 2-chloro-6-methylphenyl (87%), -methoxyphenyl (64%), p-di-ethylaminophenyl (75%), -nitrophenyl (41%), and 2-naphthyl (50%). Aliphatic isonitriles are generally best prepared by a simpler procedure involving the action of phosphorus oxychloride on an N-alkylformamide in the presence of pyridine.7... 

The proposed mechanism for formation of 151 is shown in (Scheme 27). Proton abstraction by the hydride base from the activated 2-position of the W-fluoropyridinum triflate yields a highly reactive carbene which undergoes attack by the acetonitrile solvent. The resulting nitrilium ylide eliminates fluoride and subsequently adds the isonitrile with cyclization. Finally, reduction by the hydride reagent and aromatization provide the imidazopyridine 151. The undesired amide 152 is a product of hydrolysis of the intermediate nitrilium compound. 

The retrosynthetic approach to welwitindolinone A isonitrile (6) used by the Wood group is shown in Scheme 33. After recognition of the possibility of deriving the vinyl isonitrile fragment from a ketone, the disconnection of 6 to 140 was proposed. A literature report of a samarium (II) iodide-mediated reductive coupling of acrylates with isocyanates to give amides, which could be expected to lead to a new spirooxindole synthesis, prompted the disconnection of 140 to 141. This compound was to be obtained from the readily available cyclohexadiene derivative 143, by way of bicyclic ketone 142. 

The reaction of -halo carbonyl compounds with primary amides is appropriate for oxazoles containing one or more aryl groups . Ureas form 2-aminooxazoles. Formamide can be used resulting in a free 2-position in the oxazole. A convenient synthesis of 5-substituted-4-cyanooxazoles 223 is based on the condensation of -hydroxy—cyanoenamines 222 with trimethyl orthoformate (Scheme 109). The cyanoenamine intermediates 222 are derived from Lewis acid-catalyzed Passerini reactions between /-butyl isonitrile and aldehydes <2002S1969>. 

On the basis of the same principle, we developed a three-component synthesis of macrocycles starting from azido amide (46), aldehyde (47) and a-isocyanoaceta-mide (48) (the cx-isocyanoacetamides are easily available, see [84—86]) bearing a terminal triple bond (Scheme 11) [87]. The sequence is initiated by a nucleophilic addition of isonitrile carbon to the in situ generated imine 50 led to the nitrilium intermediate 51, which was in turn trapped by the amide oxygen to afford oxazole 52 (selected examples [88-94]). The oxazole 52, although isolable, was in situ converted to macrocycle 51 by an intramolecular [3+2] cycloaddition upon addition of Cul and diisopropylethylamine (DIPEA). In this MCR, the azido and alkyne functions were not directly involved in the three-component construction of oxazole, but reacted intramolecularly leading to macrocycle once the oxazole (52) was built up. The reaction created five chemical bonds with concurrent formation of one macrocycle, one oxazole and one triazole (Scheme 15). 

In the aromatic series the direct conversion of acid amides into acid nitriles does not take place readily but the acid itself is made from the acid amide by the reverse process as indicated above, viz., by hydration to the ammonium salt of the acid, which then yields the acid. A related method, however, is used for preparing acids from anilides of formic acid. Aniline being an ammonia compound yields acid-amidelike products with aliphatic acids, e.g. acet anilide, CH3—CO—NH— CeHs (p. 556). Such a compound can not, however, lose water in the same way as the acid amide in the above reaction for the ammonia residue in an anilide contains only one hydrogen. Nevertheless anilides lose water but in a different way. In the case of the anilide of formic acid, i.e. formanilide, H—CO—NH—CeHs, the loss of water results in a compound in which the carbon and nitrogen remain linked to the benzene ring and an iso-cyanide or iso-nitrile is formed. The isonitrile is readily converted into the nitrile and the acid may then be obtained from that. 

Acid amide-triphenylphosphine dihalide adducts (4) have found wide application in organic synthesis. - Synthetic equivalents are adducts (5) from acid amides and triphenylphosphine/CCU, which are prepared in situ from the educts. - With these reagents the following transformations have been performed dehydration of amides or aldoximes to nitriles, preparation of isonitriles from secondary form-amides, preparation of imidoyl halides from amides or acylhydrazines and preparation of ketene imines from amides. Using polymer-supported triphenylphosphine the work-up procedure is much easier to achieve. Triphenylphosphine can be replaced by tris(dialkylamino)phosphines. - Instead of CCI4 hexa-chloroethane, hexabromoethane or l,l,2,2-tetrabromo-l,2-dichloroethane can be used " the adducts thus formed are assumed to be more effective than those from the triphenylphosphine/CCU system. 

Adducts (6) and (7) from amides and chlorophosphoric acid aiyl esters or dichlorophosphoric acid aryl esters respectively are well known. - The adducts are formed in a 1 1 ratio. They have been applied to the synthesis of mixed anhydrides from diarylphosphoric acids and carboxylic acids, as well as mixed substituted esters of pyrophosphoric acid. The adduct formation between primary or secondary carboxamides and dichlorophosphates has been used to prepare nitriles and isonitriles respectively. The adduct from DMF and phenyldichlorophosphate is a useful reagent for the preparation of carboxylic acid esters from the corresponding acids and alcohols, 3-lactams from imines and carboxylic acids," carboxylic acid anhydrides, carboxylic acid esters and thiol esters. Adducts of amides with ester amides or diamides of chlorophosphoric acid have been studied. ... 

A still unresolved problem is the structure of the often used adducts from phosphorus trihalides and carboxylic acid amides, which might be described by the formulae (8) or (9). With the aid of in situ generated adducts of acid amides and PX3 amidines, isonitriles, quinazolinones, alkyl chlorides, aminomethylenediphosphonic acids, carbamoyl halides, triformylaminomethane, 1,3,4-oxadia-zoles, sulfides (from sulfoxides), nitriles (from primary nitro compounds)" and bromoqui-nolines (from methoxyquinolines)" have been prepared. 

Sulfonyl halides (e.g. benzenesulfonyl chloride) form adducts (11) with acid amides in an equilibrium reaction. From these adducts or via adducts of this type 0-sulfonated lactim ethers, isonitriles, adenine, nitriles, amidines, amidinium salts and formic acid esters were prepared. The adducts from DMF and chlorosulfonamides (12) can be used to prepare amidines or amidrazones. A/-Chlorosulfonylcarboxylic acid amides yield nitriles on treatment with DMF or other tertiary amides, presumably via an acid amide sulfonyl chloride complex (13 equation 3). ... 

Phosgene, as well as the easier to handle diphosgene (chloroformic acid trichloromethyl ester) or triphosgene (carbonic acid bis(trichloromethyl) ester) transform primary, secondary and tertiary amides and thioamides to chloromethyleneiminium chlorides (25 equation 15), whereby the reaction with thioamides is of broader scope and proceeds with fewer side reactions. The amide chlorides derived from primary and secondary amides can lose HCl, giving nitriles or imidoyl halides, respectively. /V-Sub-stituted formamides can be converted to isonitriles via amide halides. ... 

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