Amides, vinylogs

The general method for preparation of heterocyclic enamino ketones, amide vinylogs, consists of a cyclization reaction (Scheme 6). The most convenient technique involves heating the starting substance in acetonitrile in the presence of silver perchlorate 137-139). 

The action of oxonium salts on vinylogous amides affords iminium salts (71 equation 44), which are useful for synthetic purposes in heterocyclic chemistry. ° " - Alkyldiphenylsulfonium tetrafluoro-borates (72 equation 45) were recommended as reagents which alkylate amides and lactams under smooth conditions.2 2 With the aid of fluorosulfonic acid esters as well as with trifluorometh-anesulfonic acid esters, - - which have alkylation power comparable to oxonium salts, iminium salts, e.g. (73) and (74 Scheme 5), could be synthesized from amides, - vinylogous amides and lactams. Trimethylsilyloxymethyleneiminium salts (75 equation 46) are accessible by reacting tri-methylsilyltrifluoromethanesulfonate with amides. - ... 

Vinylogs (Vinylogous) s. carboxylic acid amides, vinylogous... 

However, the reaction of 2,3-dimethylquinoxaline 51a with maleic anhydride 46a under standard conditions (Taylor and Hand 1963) takes place with the formation of a compound with the empirical formula C14H12N2O3, the IR spectrum of which does not contain bands for the stretching vibrations of the anhydride groups but there are bands for the stretching vibrations characteristic of NH, the OH of the carboxyl function, the double bond, and an amide vinylog (Scheme 3.16). The NMR spectra and the chemical properties of the adduct show that pyrrolo[l,2-a]quinoxaline 52a is formed as a result of the reaction, and this can be represented by the Scheme 3.16 (Taylor and Hand 1962, 1963). Accordingly, the condensation of maleic anhydride with 2-methylquinoxaline and 2-methyl-3-phenylquinoxaline gives 2-carboxymethyl- 52b and 2-carboxymethyl-4-phenylpyrrolo[l,2-a] quinoxalin-l(5H)-ones 52c (Taylor and Hand 1963 Taylor and Cheeseman 1964). 

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