Methyleneiminium salts

Enolate-Mediated Mannich Reactions with Methyleneiminium Salts... 

Methyleneiminium salt (127) and a number of carbonyl compounds 26 381 have been reacted with free aminodyne or its salts 72 (127, 128) ... 

Substituted)aminothiadiazole 1,1-dioxides 124 and 89b have been obtained respectively from a-ketoimidoyl chlorides (83JHC82I) or from chloro(ethoxycarbonyl)methyleneiminium salts (79TL2827) and sulfamides (Scheme 46). 

The reactions of alkene derivatives that do not possess electron-releasing substituents with chloro-methyleneiminium salt (1) are illustrated for some representative examples in Scheme 3. Electrophilic... 

The Mannich reaction has been reviewed comprehensively by Blicke (1942), Reichert (1959), Hell-mann and Opitz (1960), and Tramontini (1973). These reviews also include synthetic applications of Mannich bases. Mechanistic studies of the Mannich reaction have been reviewed by Thompson (1968). Some variants of the Mannich reaction have been covered as subtopics in other reviews for example. Layer (1963) and Harada (1970) have reviewed general additions of stabilized carbanions to imines, while Bdhme and Haake (1976) have reviewed similar additions to methyleneiminium salts. In more specific reviews, Pai and coworkers (1984) have summarized stabilized carbanion additions to 3,4-dihy-droisoquinolines and 3,4-dihydroisoquinolinium salts in connection with the total synthesis of protober-berines and phthalide isoquinolines, and Evans et al. (1982) " have analyzed the stereochemical aspects of ester enolate and silyl ketene acetal additions to imines. 

Pioneering investigations by Bdhme et al. into the synthesis, properties and reactions of preformed iminium salts have provided much of the basis for their recent applications in organic synthesis. These and related investigations are described in his extensive review on Methyleneiminium Salts , covering woric up to the early 1970s. 

Competition data for the trifluoroacetylation of a number of heterocycles using trifluoroacetic anhydride at 75 C give the relative rates thiophene (1.0), furan (1.4 x 10 ), 2-methylfuran (1.2 x 10 ) and pyrrole (5.3 x 10 ). Similar values, thiophene (1.0), furan (3.0 x 10 ) and pyrrole (5.0 x 10 ) are obtained for reactions with [C6H7Fe(CO)3]. We have already discussed the fact that thiophene does undergo the Mannich reaction using preformed methyleneiminium salts and therefore it is not surprising that furan also affords the aminomethyl derivatives in reactions with iminium salts. 

The yields of the Mannich bases obtained when a number of methyleneiminium salts were allowed to interact with furan in acetonitrile at room temperature ranged from 66 to 74%. ° A representative example is shown in equation (28). The reasons for the earlier failures remain obscure but the amine would not have been lost under the aqueous reaction conditions. 

Preformed methyleneiminium salts react with 2-methylfuran to give the expected products in 65-94% yield. It is even possible to carry out a reaction with A A -diisopropylmethyleneiminium chloride (equation 29), the latter reagent being prepared in excellent yield by the interaction of ethoxy-A(,A(-diisopropyl-aminomethane with trichloromethylsilane. 

Aminations which afford 6-aminocarboxylates are of interest in relation to monobactam antibiotics. A secondary aminomethyl group can be introduced at the -position of carboxylic esters by reaction of hexahydro-1,3,5-triazines with ketene silyl acetals in the presence of a catalytic quantity of trifluoromethanesulphonic acid (Scheme 25). The triazine (10) is considered to be converted into an N-silylated methyleneiminium salt which undergoes addition of the ketene silylacetal (11). 

The synthesis of a-halogenated imino-compounds has been reviewed, and the preparation of chloro(ethoxycarbonyl)methyleneiminium salts as versatile intermediates in heterocyclic synthesis has been demonstrated. ... 

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