Abstract
A series of 2-aryl substituted hexahydropyrimidines and perimidines were synthesized from aromatic aldehydes and substituted 1,3-propanediamines or 1,8-naphthalenediamine. The 1H and 13C NMR spectra showed that 2-arylperimidines and 2-aryl-4,4,6-trimethylhexahydropyrimidines exist exclusively in ring forms even in DMSO solutions, whereas 2-aryl-4-methylhexahydropyrimidines undergo chain-ring-chain tautomerism with a good linear correlation between the ring-chain equilibrium constants (log K, where K=[ring]/[chain]) and the Hammett–Brown σ + parameters of the aromatic substituents. 4,4,6-Trimethylhexahydropyrimidines underwent complete and irreversible ring opening in CF 3COOH solutions giving two different chain forms.
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