Substituent effects in the ring-chain tautomerism of 4-aryl-1,3,4,6,7,11b-hexahydro-2H-pyrimido[6,1-a]isoquinolines

One-step route to tricyclic fused 1,2,3,4-tetrahydroisoquinoline systems via the Castagnoli–Cushman protocol

“…As it is known, the benzo[a]quinolizidine system can exist as interconvertible conformers due to the presence of a stereo- chemically mobile nitrogen atom [41]. Numbers of studies suggested that the preferred conformation of benzo[a]quinolizidines depended strongly on the type of substituents, the presence of stereocenters and their configuration [36,[41][42][43][44][45][46]. As for the 4-oxobenzo[a]quinolizidine derivatives, it should be noted that due to the planar amide fragment the interconversion of the different conformers could be largely suppressed.…”

A comparison of the electron ionization and electrospray behaviour of some N,N′‐disubstituted hexahydropyrimidines

“…In organic synthesis, the hexahydropyrimidine nucleus has been employed as a protecting group in selective acylations and additions of 1,3‐diamines, due to its easy cleavage in mild acidic medium,11, 12 while some derivatives are synthetic intermediates for antineoplastic drugs and structural units in new trypanothione reductase inhibitors 13, 14. Some recent reports have been devoted to the study of ring‐chain tautomerism in hexahydropyrimidines,15–17 their benzo‐fused derivatives (1,2,3,4‐tetrahydroquinazolines),18 and related compounds 19–21…”

“…discussed the fragmentation of some tricyclic hexahydropyrimidines (tetraponerines) isolated from natural sources 9. More recently, mass spectrometry was employed to assess the presence of chain tautomers in N‐unsubstituted hexahydropyrimidines and related compounds 17, 21. To our knowledge, data concerning electrospray ionization (ESI) mass spectra of hexahydropyrimidines have not previously been reported.…”