Novel Syntheses of the Major Flavor Components of Bread and Cooked Rice

Abstract

A new synthetic pathway toward the Maillard flavor compounds 6-acyl-1,2,3,4-tetrahydropyridines and 2-acetyl-1-pyrroline is presented. The reaction sequence involves deprotonation of a vicinal diimine and subsequent alkylation with an N,N-diprotected ω-bromoalkylamine, followed by deprotection and intramolecular transimination of the functionalized intermediate. Acidic workup affords the above-mentioned heterocycles, which are principal flavor constituents of bread and cooked rice, respectively. In addition, the synthesis of the more stable diethyl acetal of 2-acetyl-1-pyrroline is described.

Thirty-three years of 2-acetyl-1-pyrroline, a principal basmati aroma compound in scented rice (Oryza sativaL.): a status review

“…A straightforward synthesis of 2AP was reported by De Kimpe and co‐workers . They also reported synthesis of 2AP by deprotonation of a vicinal diamine and subsequent alkylation with an N,N‐diprotected ω ‐bromoalkylamine, followed by deprotection and intermolecular transamination of the functionalised intermediate . In addition they also synthesised diethylacetal of 2AP which was more stable.…”

“…They further claimed that 2AP can remain stable for up to 2 years as a picrate . De Kimpe and Keppens synthesised the diethylacetal of 2AP which was claimed to be more stable . Srinivas and co‐workers successfully stabilised this compound for more than 1 year by making a derivative of 2AP using acids…”

Quantification of 2-acetyl-1-pyrroline in rice by stable isotope dilution assay through headspace solid-phase microextraction coupled to gas chromatography–tandem mass spectrometry

“…Many synthetic routes to 2-acetyl-1-pyrroline have been described in the literature [9,[31][32][33][34][35][36]. However, all of them suffer of the difficulty to be effectively transposed to an isotopic labelling strategy because of long, fastidious and/or costly synthetic protocols.…”

“…SPME procedures developed so far for the quantitative analysis of 2AP from rice did not involve such approach. Indeed the methods described hitherto for the synthesis of 2AP and its labelled analog were long and fastidious [9,[31][32][33][34]. In the present work a new and simple method for the synthesis of both compounds has been undertaken.…”

Product Class 7: Imines

“…In a second step, desilylation of ø-amino imines 104 using tetrabutylammonium fluoride, or methanolysis in the presence of potassium carbonate, finally results in a transimination reaction to give the cyclic imines 105 (Scheme 40). Similarly, 2-azaspiroimines, [390] the flavor compounds 5-acetyl-3,4-dihydro-2H-pyrrole and 6-acetyl-2,3,4,5-tetrahydropyridine, [391] dihydroindoles, tetrahydroquinolines, [392] and the alkaloid polonicumtoxin C [158] have been made available.…”