Studies toward the synthesis of cinachyramine. An efficient route to 1,5-diazabicyclo[4.4.0]dec-5-enes.

Hydrogenation (3 atm) of readily available pyrido[1,2-a]pyrimidines 10, 14, and 17 over 5% Rh/Al2O3 forms 1,5-diazabicyclo[4.4.0]dec-5-enes 9, 15, and 18 in > 95% yield, providing a general route to this little-studied class of compounds. All attempts to form the tetrahydro-1,2,4-triazine moiety of cinachyramine (1) by rearrangement of amidinium dimethylhydrazone 8 using the procedures developed by Kamatori to convert hydrazone 3a to tetrahydro-1,2,4-triazine 4a were unsuccessful.