1,3‐Oxathianes, Chiral Fruit Flavour Compounds

Abstract

From optically pure 3-mercaptohexan-1-01s as key intermediates some chiral 1,3-0xathianes were synthesized and their structures elucidated by 'H and 13C NMR spectra. Sensory qualities of the optically pure isomers are given. 1,3-Oxathiane, chirale Fruchtarorna-VerhindungenMit optisch reinen 3-Mercaptohexan-1-olen als Schliisselsubstanzen werden einige chirale 1,3-0xa-thiane synthetisiert und ihre Strukturen mittels 'H-und "C-NMR-Spektren bestimmt. Die sensorischen Qualitaten der optisch reinen lsomere werden angegeben.3-(Methylthio)hexan-l-ol (2) and 2-methyl-4-propyl-I ,3-oxathiane (3), isolated and revealed in constitution by Winter et al.'") were found to be characteristic aroma compounds in the yellow passion fruit (Pussifloru edulis, f. flavicarpa). With optically pure 3-mercaptohexan-1-01s ( l a , 1 a') as key intermediates recently we succeeded in synthesizing all the four stereoisomers of 32-4). Some times later Pickenhagen et al.5) reported their efforts for enantioselective synthesis of (-)-and (+)-cis 3. In this work we present our latest results on structure function relationship of some chiral 1,3-oxathianes, well known fruit flavouringsIb), but up to the present without knowledge of their optical purity.By introduction of the acetyl rest the primary alcoholic function of 1 was protected and the 3-mercapto group esterified with chiral acyl chlorides [e. g . (-)-camphanoyl chloride2)] to give the diastereomeric thiol esters which were separated by liquid chromatography and transferred into the enantiomers l a and la' by reductive cleavage with LiAlH,. Absolute configurations of l a and la' were derived from 'H NMR spectroscopic behaviour of their hydratropic acid thiol esters2s3). This method proves the ( -) -( R ) and (+)-(S) configuration of the optical isomers l a and la', respectively. From cyclization of the key intermediates l a and la' with acetaldehyde result the optically pure cis/truns diastereomers 3a/3b and 3a'/3b' (10: I), respectively, which were separated by HRGC on SE 54 and in preparative scale by HPLC on C N phase. In a similar manner condensation of l a (la') with acetone or formaldehyde leads to the enantiomers of 2,2-dimethyl-4-propyl-l,3-oxathiane (4) or 4-propyl-I ,3-oxathiane (5), respectively. The main products 3a and 3a' of the 10: 1 mixtures of 3 were assumed to correspond to the thermodynamically more stable cis isomers'). But unambiguous conclusions for structure elucidation can be drawn from high-resolution 'H NMR spectroscopy (400 MHz).

Identification of new sulfur-containing volatiles in yellow passionfruit (Passiflora edulis f. flavicarpa)

“…34Methylthio) hexanol and a mixture of cis-and trans-2-methyl-4-propyl-l,3-oxathiane and the corresponding oxide, 2-methyl-4-propyl-173-oxathiane %ox-ide (Winter et al, 1976; Winter, 1980), have been described as key ingredients for the aroma of the yellow passion fruit (Passiflora edulis f. flavicarpa). A strong influence of the configuration of these chiral volatiles on their sensory properties has been demonstrated (Heusinger and Mosandl, 1984; Pickenhagen and Bronner-Schindler, 1984; Mosandl and Heusinger, 1985). The naturally occurring configuration of cis-2-methyl-4-propyl-l,3-oxathiane in the yellow passion fruit has been determined (Singer et al, 1986).…”

Chirality in flavor chemistry‐recent developments in synthesis and analysis

“…These methods are of some interest for the stereochemical analysis of chiral alkan-l,3-diols and monothio-l,3-glycols (Fig. 9), which are important with respect to their role as key intermediates for the synthesis of optically pure 1,3-dioxanes and 1,3-oxathianes (56,57). In principle this method allows stereodifferentiation for all classes of chiral substances, which can be reduced by LiAlH 4 to products with chiral secondary alcoholic functions.…”

“…This method proves the (R)(-) and (5)(+) configuration of the optical isomers 13a and 13a', respectively. Cyclization of these key intermediates with acetaldehyde results in the optically pure cis/trans diastereoisomers 14a • b and 14a' • b', which were separated by LC methods (57).…”

75 Jahre Riechstoff‐und Aroma‐Chemie im Spiegel der Helvetica Chimica Acta.Teil II

“…113). Diese Ergebnisse wurden an den enantiomerenreinen Verbindungen 8 und 9 bestatigt und auf das entsprechende trans-l,3-Oxathian-Derivat erweitert [452]. Einen Meilenstein auf dem Gebiet der enantioselektiven Geruchswahrnehmung bedeuteten die Ergebnisse beim Nootkaton (Fig.…”