Reissert compounds under acidic conditions

A new synthesis of dibenzo[a,g]quinolizinium derivatives also makes use of an aldehyde cyclization (Scheme 80) (75JAP(K)7596599). In one example, a benzyl bromide bearing an acetal-masked aldehyde group in the ortho position (126) was allowed to react with the anion (127) generated by the action of phenyllithium on a Reissert compound. The condensation product was heated with alkali to cleave the benzoyl and cyano groups to yield the isoquinoline (128), then the acetal was cleaved and the resulting aldehyde cyclized to (129), presumably under acid conditions. 

The previously described Reissert compounds (94) can be converted back to the original heterocycles (91) by sodium hydroxide or, more usefully, by sodium hydride to the nitrile substituted heterocycles (100) <92CPB5137>. Under acidic conditions fission of the dihydropyrimidine ring occurs to give the triazole (101). V-Nitration of the tetrahydro[ 1,2,5]oxadiazolo[3,4-6]pyrazine (102) gives the explosive dinitro compound (67) (Scheme 7) <85J0C5123>. 

Treatment of the compounds 78 with various alkyl halides in the presence of sodium hydride results in 1-alkylation as with normal Reissert com-pounds. ° Acylation has also been reported under these conditions. Under a variety of conditions, however, 78 does not react with benzaldehyde. Acid hydrolysis of 80 gave tetrahydroquinaldic acid, while acid hydrolysis of the alkylated dihydroisoquinoline-Reissert compounds gave the amino acids 81. By first complexing the alkylated dihydroisoquinoline-Reissert compound with zinc chloride in ether and then hydrolyzing the complex, the nitrile was hydrolyzed to an acid, but the amide group was left intact. The perchlorate salts of dihydroisoquinoline-Reissert compounds have also been prepared, and sodium borohydride reduction proceeds in the same manner as reduction of the Reissert salt to... 

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