Amidinium salts 7,8-unsaturated

Amidinium salts can also serve as starting materials for transamination reactions, e.g. Scheme 17 7.14,314 ji g condensation of orthoamides with amidinium salts containing a-CH2 groups af fords a,p-unsaturated amidinium salts, e.g. (144 equation 86). ... 

Unsaturated macrolides such as (115) or (117) (Scheme 38) have been synthesized by Eschenmoser using a fragmentation reaction as a key step. The tricyclic ketal carboxylate (114) can be cleaved as an amidinium salt to give (115) in excellent yield simply on heating. Similarly, the macrolide (117) with ( , )-configuration is obtained from (116). This decarboxylative double fragmentation represents a nine-center Grob type. 

Other synthons for 1,3-dicarbonyl compounds that have been successfully applied include p-chloro-a,P-unsaturated ketones and aldehydes, P-dimethylamino-a,P-unsaturated ketones (easily obtained from ketones by reaction with DMFDMA), P-alkoxy-enones"" and vinyl-amidinium salts."" Alkynyl-ketones react with 5-alkyl-isothioureas, giving 2-alkylthio-pyrimidines" and propiolic acid reacts with urea to give uracil directly in about 50% yield. "" 1,3-Keto-esters with formamidine produce 4-pyrimidinones"" and C-substituted formamidines with ethyl cyanoacetate give 2-substituted-6-amino -pyrimidinones. In analogy, pyrimidines fused to other rings, for example as in quinazolines, can be made from ortho-aminonitriles " and in general, from P-enamino esters. ... 

Reactions of 2-formyl-galactal, presented as an unsaturated sugar derivative with push-pull functionalization, with guanidinium and amidinium salts, respectively were carried out imder basic conditions to furnish the substituted 5-( 1,2,4-tri-O-benzyl-D-lyxo- l,2,3,4-tetrahydroxy-butyl)pyrimidines 92 (Fig. 16). Treatment of the 2-formyl pentose glycals with 2-aminobenzimid-azole and 3-amino-1,2,4-triazole, respectively afforded 3-(l,2,4-tri-0-benz-yl-D-lyxo-l,2,3,4-tetrahydroxy-butyl)benzo[4,5]imidazo[l,2-a]pyrimidine 94... 

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