Synthesis of 2-acetyl-1-pyrroline, the principal rice flavor component

Abstract

A new straightforward synthesis of 2-acetyl-l-pyrroline, the principal rice flavor component with a cracker-like flavor, is reported. The reaction sequence involves the conversion of pyrrolidine into tripyrroline, subsequent hydrocyanation of the latter into 2-cyanopyrrolidine, oxidation into 2-cyano-1-pyrroline, and Grignard addition of methylmagnesium iodide, affording an overall yield of 16-19% from pyrrolidine. In similar way, 2-propionyl-l-pyrroline, a recently discovered flavor component of popcorn, was prepared in addition to several higher analogues, i.e., 2-acyl-1-pyrrolines. Also, the synthesis of 2-(acetyl-da)-1-pyrroline, a deuterated derivative of the rice flavor compound which is useful for the stable isotope dilution assay, is described.

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

“…2-Acetyl-1-pyrroline (6) was isolated from this mixture via preparative gas chromatography. All spectral data ( 1 H and 13 C NMR, IR, MS) were identical to data reported in the literature (De Kimpe et al, 1993a). As mentioned above, no traces of the enamino form of 1-pyrroline 6 could be detected ( 1 H and 13 C NMR).…”

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.…”

“…The determinant step in the synthesis described by De Kimpe et al [35] was the lateral chain deuteration through the introduction of methylmagnesiumd 3 iodide on the 2-cyano-1-pyrroline. Besides the difficult synthesis of this 2-(acetyl-d 3 )1-pyrroline, a problem of labelling stability was encountered because a deuteration on an alpha position to a carbonyl group leads to proton/deuterium exchange with protogenic solvents.…”

“…Besides the difficult synthesis of this 2-(acetyl-d 3 )1-pyrroline, a problem of labelling stability was encountered because a deuteration on an alpha position to a carbonyl group leads to proton/deuterium exchange with protogenic solvents. On the other hand, a 13 C-labelled analog of 2-acetyl-1-pyrroline was prepared to obtain 2-acetyl-( 13 Cmethyl)-1-pyrroline by Yoshihashi et al [36], according to the same method of De Kimpe et al [35].…”

Analysis of Freshly Brewed Espresso Using a Retronasal Aroma Simulator and Influence of Milk Addition

“…The preparation of 2,3-dihydro-6-methylthieno[2,3c]furan, and 1-(3,4-dihydro-2H-pyrrol-5-yl)-ethanone were conducted as described in the literature, respectively (Buchi et al, 1971;De Kimpe et al, 1993). Volatile compounds were identified by comparing their mass spectra and Kovats indices using C 6 -C 28 n-alkanes to those of standard compounds and to those from the literature (Baltes and Bochmann, 1987a, 1987b, 1987c.…”