Showing papers by "Christian V. Stevens published in 1993"

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

Abstract: A new straightforward synthesis of 2-acetyl-1-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-1-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-d 3 )-1-pyrroline, a deuterated derivative of the rice flavor compound which is useful for the stable isotope dilution assay, is described

Enantioselective synthesis and determination of the configuration of stenusine, the spreading agent of the beetle Stenus comma

Abstract: The enantioselective total synthesis of two of the four possible stereoisomers of stenusine (1), the spreading agent of the beetle Stenus comma, is described. The silyl ether-substituted aldehyde SAMP hydrazone 2 was alkylated with (S)-1-bromo-2-methylbutane (3) yielding the hydrazone 4 in high diastereomeric purity (de >95 %). By several steps including the reduction of the hydrazone functionality and the cleavage of the N-N bond of the intermediates, 4 was converted into the BOC-protected amino alcohol 6. Subsequent cyclization of 6 afforded the (S,S) diastereomer of stenusine with 96.6 % de, >99.9 % ee, and in 11.3 % overall yield. Repetition of this synthesis using the aldehyde RAMP hydrazone (R)-2 as the starting material produced (SR)-1 with 95.0 % de, >99 % ee, and in 8.2 % overall yield. The synthetic samples of 1 were employed to investigate the stereochemistry of natural stenusine by means of GC analysis on both a chiral and an achiral, stationary phase. As a result of these studies natural stenusine was found to be a mixture of all four stereoisomers in a ratio of (S,S)/(SR)/(RR)/(R:S) = 43:40:13:4.

Synthesis of stenusine, the spreading agent of the beetle Stenus comma

Abstract: Stenusine [1-ethyl-3-(2-methylbutyl)piperidine], the spreading agent of Stenus comma, was synthesized by a six-step sequence in 21 % overall yield from acetaldehyde. Acetaldehyde was converted into the corresponding N-tert-butyl aldimine, which was sequentially alkylated via its 1-azaallylic anion with 1-bromo-2-methylbutane and 1-bromo-3-chloropropane. The resulting delta-chloro aldimine was hydrolyzed into the delta-chloro aldehyde, which was converted into the corresponding N-ethyl aldimine. The latter labile delta-chloro aldimine was cyclized with lithium aluminum hydride to afford stenusine. The 1-tert-butyl analogue of stenusine was synthesized using an analogous route.

Synthesis of 2-alkyl- and 2-arylazetidines from β-chloroimines

Abstract: 2-Alkyl- and 2-phenylazetidines are synthesized by treatment of N-(3-chloro-2,2-dimethylpropylidene)amines with alkyllithium and phenyllithium reagents, respectively. Addition of the organometallic reagent across the imino bond of the β-chloroimine is followed by intramolecular nucleophilic substitution yielding 2-substituted azetidines