This invention relates to the functionalization of acylpyridinium salts in a chemoselective and regioselective manner. A problem faced in such syntheses involves introducing a carboalkoxyalkyl group regio and chemoselectively onto a functionalized pyridine ring system. There have been isolated reports of the addition of a carboethoxymethyl group to a unsubstituted pyridine ring employing either the Reformatsky reagent derived from ethyl bromoacetate or the titanium enolate of ethyl acetate to yield a mixture of 1,2 and 1,4 dihydropyridines in moderate yield.sup.2a,b. However, chemoselectivity is a problem with these reagents because of their tendency to add to carbonyl compounds (vide infra).
Other workers.sup.1,9 have used Grignard reagents to prepare 1,2 dihydropyridines, however chemoselectivity is a problem because such reagents also tend to add to carbonyl compounds.
A report by Yamaguchi et.al.,.sup.3 demonstrated that allyltin reagents are sufficiently nucleophilic to add to acyl pyridinium salts in a regio and chemospecific manner.
USPTO Backgrounds
USPTO Backgrounds