Reactions of Ph(2)C(3) dianion, prepared from 1,3-diphenylpropyne and n-butyllithium, with alkyl thiocyanates or alkane dithiocyanates gave 1,3-bis(alkylthio)allenes 1 or tetrathiacyclic bisallenes 2, respectively. Thermal reactions of 1 gave thiophenes 4 and 7, benzothiepin 5, 1,2-bis(benzylidene)cyclobutane 6, thiete 8, and alpha,beta-unsaturated ketone 9, and the reactions of tetrathiacyclic bisallenes 2a gave a cyclic dimer, 1,2-bis(benzylidene)cyclobutane derivative 10, quantitatively. Irradiation of 1,3-bis(alkylthio)allenes 1 and tetrathiacyclic bisallenes 2a caused rearrangement to give alkynes 18, 20, and 21. In the irradiation of the cyclic bisallenes 2a, isomerizations from dl to meso and meso to dl isomers were also found. In the reactions of allenes 1 and cyclic bisallenes 2a with diphenyl diazomethane, the diazomethane reacted selectively with the double bond rather than with the sulfur atom.

Introduction Flowering of the Asian skunk cabbage (Symplocarpus renifolius, Araceae) shows a sequential expression of female, bisexual and male sex phases. The protogynous thermogenic inflorescence has unpleasant odours, but the contributing chemical composition is poorly understood. Objective To determine the volatile composition of odour emissions from each S. renifolius flowering phase. Methodology The dynamic headspace method was used to collect floral volatiles from six intact S. renifolius inflorescences in their natural habitat. Collected volatiles from the three flowering phases were analysed using gas chromatography–mass spectrometry/olfactometry (GC–MS/O). Results Female‐phase inflorescences were characterised by an earthy‐rotten‐minty odour, while male‐phase inflorescences typically exhibited a rotten‐oily odour. Approximately 160 compounds were detected in volatiles from the three phases. Common to all phases were 3‐methylbutyl 3‐methylbutanoate, 1,8‐cineole, dimethyl disulphide and sabinene, together accounting for 52 to 54% of total volatiles. GC–MS/O revealed that at least 28 volatiles including eight S‐containing compounds contributed to the unpleasant odour of S. renifolius. Among them, dimethyl disulphide (onion‐like), methional (potato‐like), and the tentatively identified methyl dithioformate (garlic‐like) were intense odour‐active compounds in each floral phase. Additionally, 2‐isopropyl‐3‐methoxypyrazine (IPMP) was a major contributor to the earthy odour that was characteristic of the female phase. Conclusions No marked changes were observed in floral volatile compositions over the three flowering phases of S. renifolius. Instead, flower phase‐dependent proportional changes of minor components (e.g. IPMP and 2,3‐butanedione) altered the odour characteristics between the female and male phases.

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A test apple beverage made up of apple juice (20%), high-fructose corn syrup (11.5%), citric acid (0.43%), trisodium citrate (0.02%), apple-odor flavor (0.1%), and ascorbic acid (0.02%) was stored at 40 °C and then analyzed for the change of odor in the beverage. Although no thermoacidophilic bacteria (TAB) were detected, a medicinal off-flavor was perceived after the 8 weeks of storage. Model experiments on the ingredients of the test apple beverage revealed that the off-flavor compound had been formed by ascorbic acid and (E)-hex-2-enal. Synthesis and NMR (¹H, ¹³C, HMQC, and HMBC) analyses identified the compound as 6-propylbenzofuran-7-ol. The odor quality, retention index (RI), and mass spectrum of synthetic 6-propylbenzofuran-7-ol were identical with those of the medicinal odor compound from the test apple beverage. Sensory evaluation revealed the recognition thresholds for medicinal odor were 31.4 ppb in water and 24.0 ppb in apple beverage, and the detection thresholds were 19.6 ppb in water and 8.6 ppb in apple beverage, respectively. The quantified concentration of 6-propylbenzofuran-7-ol formed in test apple beverage was 90 ppb, approximately. This concentration was well above the odor threshold, so it was concluded that the compound was the source of the medicinal off-flavor.

In a previous work, we identified 6-propylbenzofuran-7-ol as an off-flavor compound formed from ascorbic acid and (E)-hex-2-enal in a test apple beverage. In this study, we elucidate the pathway by which 6-propylbenzofuran-7-ol formed. Isotope labeling studies revealed that the propyl group of 6-propylbenzofuran-7-ol derives from (E)-hex-2-enal and that 6-propylbenzofuran-7-ol contains carbons 2-6 of ascorbic acid. Two compounds, namely, 2,3-dihydro-6-propylbenzofuran-3,7-diol and 3-(2-furoyl)hexanal, were identified as byproducts of a model reaction of ascorbic acid and (E)-hex-2-enal. Each of these compounds was dissolved in an aqueous solution of citric acid and stored at 60 °C for 1 week. After storage, 6-propylbenzofuran-7-ol was detected from a solution of 2,3-dihydro-6-propylbenzofuran-3,7-diol, but not from 3-(2-furoyl)hexanal. 6-Propylbenzofuran-7-ol was formed by isolating tricyclic hemiacetal lactone derived from the Michael addition of ascorbic acid to (E)-hex-2-enal, mixing the tricyclic hemiacetal lactone with the aqueous solution of citric acid, and applying heat. This confirmed that 6-propylbenzofuran-7-ol was formed via the Michael adduct.