6-Acetyl-2,3,4,5-tetrahydropyridine and 2-acetyl-1-pyrroline are usually formed by Maillard reactions during heating of food. Both compounds have odor thresholds below 0.06 ng/L.[1][2]
^T. J. Harrison, G. R. Dake (2005). "An expeditious, high-yielding construction of the food aroma compounds 6-acetyl-1,2,3,4-tetrahydropyridine and 2-acetyl-1-pyrroline". J. Org. Chem.70 (26): 10872–10874. doi:10.1021/jo051940a. PMID16356012.
^De Kimpe, Norbert; Stevens, Christian (1993). "A convenient synthesis of 6-acetyl-1,2,3,4-tetrahydropyridine, the principle bread flavor component". Journal of Organic Chemistry. 58 (10): 2904–2906. doi:10.1021/jo00062a042.