Carboxamides, dehydration secondary

Chlorination and Dehydration of Substituted Carboxamide Groups. Secondary amides and A, N,Af-trisubstituted ureas possessing an N-H bond are converted to imidoyl chlorides - and... 

The addition of Grignard reagents to aldehydes, ketones, and esters is the basis for the synthesis of a wide variety of alcohols, and several examples are given in Scheme 7.3. Primary alcohols can be made from formaldehyde (Entry 1) or, with addition of two carbons, from ethylene oxide (Entry 2). Secondary alcohols are obtained from aldehydes (Entries 3 to 6) or formate esters (Entry 7). Tertiary alcohols can be made from esters (Entries 8 and 9) or ketones (Entry 10). Lactones give diols (Entry 11). Aldehydes can be prepared from trialkyl orthoformate esters (Entries 12 and 13). Ketones can be made from nitriles (Entries 14 and 15), pyridine-2-thiol esters (Entry 16), N-methoxy-A-methyl carboxamides (Entries 17 and 18), or anhydrides (Entry 19). Carboxylic acids are available by reaction with C02 (Entries 20 to 22). Amines can be prepared from imines (Entry 23). Two-step procedures that involve formation and dehydration of alcohols provide routes to certain alkenes (Entries 24 and 25). 

It should be noted that Jochims and coworkers first carried out the reaction starting from carboxamides139,140. Until recently almost no acylated persubstituted amidinium salts 306 were obtained by reaction of nitrilium salts with tertiary carboxamides 305 (equation 84). Starting from secondary carboxamides 307, mixtures of A1-acylated A A -disubstituted amidinium salts 308 and 309 are isolated (equation 85). Primary carboxamides 310 undergo dehydration by the nitrilium hexachloroantimonates 290 to... 

Poly(styryldiphenylphosphine) (8) in carbon tetrachloride converts alcohols to alkyl chlorides up to 20 times faster than does triphenylphosphine, as shown in equation (5). The phosphine oxide by-product is easily separated by filtration, but it cannot be recycled due to concurrent formation of a dichloromethylidinephosphorane. Yields are about 90% from primary and 40-70% from secondary alcohols. Reagent (8) in carbon tetrachloride also dehydrates primary carboxamides and oximes to amines, and secondary carboxamides and oximes to imidoyl chlorides. ... 

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