Quinolizine sulfur derivatives

In methanol, isoquinoline and the ester gave the benzo[fif]indolizine [(121), cf. Section II,D,3] while in ether the labile adduct, tetra-methyl llbH-benzo[a]quinolizine-l,2,3,4-tetracarboxylate (122) was obtained. The labile adduct is much less easily isoraerized than the 9-methyl-9aH-quinolizines derived from pyridines (Section III,F,1) but with boiling xylene or, better, with sulfuric-acetic acids the cor-... 

The cathodic cyclization of several types of A -(5-oxoalkyl)pyridinium salts in 1 M sulfuric acid afforded quinolizine derivatives. For example, compound 256, prepared from 4-methylpyridine, gave a diastereomeric mixture of quinolizines 257 and 258. Differential pulse polarographic studies allowed a mechanism to be proposed, which is outlined in Scheme 53 <2003EJ02919>. 

Treatment of the ethylene ketals 49 (R = H or Me) with acid gives the N-oxides 50. The use of concentrated sulfuric acid, however, produces the quinolizine 51, rather than the expected fused pyrazine, from the ketal 49 (R = Et). The nitrile 52 on reaction with bromoacetaldehyde oxime (53) in dry acetonitrile yields the imino compound 54 without isolation of the intermediate quaternary salt. The imino compound is hydrolyzed by aqueous acid to the oxo derivative 55. 

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