Tetrahydropyridine

Tetrahydropyridines are heterocycles with the formula. Three isomers exist, which differ by the location of the double bond. None of the parent species occur widely, so they are mainly of theoretical interest. Although the parent tetrahydropyridines are rare, many substituted tetrahydropyridines are known.

Preparation and occurrence

2,3,4,5-tetrahydropyridine, a colorless liquid, is commercially available. It is an imine and readily trimerizes, forming the hexahydro-1,3,5-triazine and fused hexahydro-1,3-diazine derivatives α-, β-, and iso-.
6-acetyl-2,3,4,5-tetrahydropyridine contributes to the flavor of baked goods such as bread.

N-Alkyl derivatives

While true tetrahydropyridine are rare, N-alkyl derivatives are more common. Partial reduction of pyridinium salts gives N-alkyltetrahydropyridines. Treatment of N-methylpyridinium salts with borohydride reagents gives 1-methyl-1,2,3,6-tetrahydropyridine.
A modified Ireland-Claisen rearrangement leads to tetrahydropyridines via a silyl ketene acetal intermediate.
Ring-closing olefin metathesis has also been used to establish the tetrahydropyridine ring system.