An expedient phosphine-catalyzed [4 + 2] annulation: synthesis of highly functionalized tetrahydropyridines.
Ethyl 2-methyl-2,3-butadienoate acts as a 1,4-dipole synthon and undergoes [4 + 2] annulation with N-tosylimines in the presence of an organic phosphine catalyst. The resulting adducts, ethyl 6-substituted-1-(4-tosyl)-1,2,5,6-tetrahydro-pyridine-3-carboxylates, are formed in excellent yields with complete regioselectivity. Mechanistic reasoning for this new annulation has led to an expansion of the reaction scope by employing ethyl 2-(substituted-methyl)-2,3-butadienoates to give ethyl 2,6-cis-disubstituted-1-(4-tosyl)-1,2,5,6-tetrahydro-pyridine-3-carboxylates with high diastereoselectivities.
Zhu
Xue-Feng
XF
Department of Chemistry, University of California, Los Angeles, California 90095-1569, USA.
Lan
Jie
J
Kwon
Ohyun
O
D002070:Butadienes / Q000737:chemistry; D002384:Catalysis; D003500:Cyclization; D007097:Imines / Q000737:chemistry; D010720:Phosphines / Q000737:chemistry*; D011725:Pyridines / Q000138:chemical synthesis*; D014105:Tosyl Compounds / Q000737:chemistry
D002070:Butadienes; D007097:Imines; D010720:Phosphines; D011725:Pyridines; D014105:Tosyl Compounds; C044646:phosphine