Journal of Organic Chemistry p. 4950 - 4955 (1994)
Update date:2022-08-10
Topics:
Boger, Dale L.
Kochanny, Monica J.
A detailed study of the scope of the amidine Diels-Alder reaction with 1,3,5-triazines is described.The thermal reaction of amidines with symmetrical 1,3,5-triazines proceeds with in situ amidine to 1,1-diaminoethene tautomerization, <4 + 2> cycloaddition with the 1,3,5-triazine, loss of ammonia from the initial Diels-Alder adduct with imine generation, imine to enamine tautomerization, and retro Diels-Alder loss of ethyl cyanoformate to provide substituted 4-aminopyrimidines in excellent conversions.The reaction proceeds best with the amidine hydrochloride salts at intermediate reaction temperatures (90-100 deg C) in polar, aprotic solvents, is rather invariant to the ratio of dienophile-diene used (<1:2<*>1:1<*>2:1), and is subject to triazine substituent effects characteristic of an inverse electron demand Diels-Alder reaction (R = CO2Et > R = H >> R = SCH3).Notably, the generality of the amidine <4 + 2> cycloaddition reaction with 1,3,5-triazines which has been extended to include cyclic amidines effectively addresses the limitations of the alternative ynamine or N,O-ketene acetal dienophiles.A comparative examination of amidines, thioimidates, and imidates revealed that amidines are uniquely suited for use in this reaction cascade.
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