Ar-Turmerone

Simple synthetic routes to bisabolol-3-one (35) (a-bisabololone) (c/. Vol. 6, p. 58) and ar-turmerone (36) have been achieved by condensing the kinetic enolate... 

Such routes have been used for the synthesis of natural products terpenes such as egomaketone (3-(4-methyl-3-pentenoyl)furan, perillene, ar-turmerone and iso-ar-turmerone [341], ar-curcumene [152], artemisia and isoartemisia ketones [342, 343], damascone [344], macrolides such as maysine [345], and pheromones with the sex attractant of the pine saw-fly [346],... 

The possibility of conversion of the dithioacctal into the corresponding ketone without reconjugation of the double bond is a noteworthy j feature of this synthetic scheme. The syntheses of iso-ar-turmerone and isoartemisia ketone mentioned above proceeded similarly via a carbophilic pathway. In the latter case a p-ethylenic dithioester was not isomerized during the following overall sequence carbophilic addition-methylation-dithioacetalization [343]. ... 

When R2 was a methallyl group a mixture of conjugated and unconjugated ketones was obtained. Treatment by DBU or piperidine yielded the conjugated ketone. The last example in Table 4.2 corresponds to ar-turmerone. 

Cleavage of 4-tetrahydropyrones.1 The terpene ar-atlantone (2) and the dihydro derivative ar-turmerone (3) have been obtained by cleavage of the 4-tet-rahydropyrone 1 with ClSi(CH3)3/NaI. Reaction of 1 with ClSi(CH3)3/NaI in DMF... 

The reaction provides the key step in a synthesis of ar-turmerone (2), equation... 

When the ylid derived from the oxide 7 was treated with benzaldehyde, a 2-methoxy-l,3-diene was formed. This led us to attempt a synthesis of (i) ar-turmerone by a sequence (Scheme 3) in which 7 effectively acts as an acyl anion equivalent. The required aldehyde 8 was synthesized in good yield using initially diphenyl(methoxymethyl)phosphine oxide (3), and then chlorotri-methylsilane-sodium iodide (12) to cleave the enol ether. 

Mori, K. (2005). Synthesis of (R)-ar-turmerone and its conversion to (R)-ar-himachalene, a pheromone component of the flea beetle (R)-ar-himachalene is dextrorotatory in hexane, while levorotatory in chloroform. Tetrahedron Asymmetr., 16, 685-692. 

Dried rhizomes and leaves are used industrially to extract the volatile oil. Dried rhizomes contain 5-6% and leaves contain about 1.0-1.5% oil. Generally, the oil is extractedby steam distillation. Supercritical extraction using liquid carbon dioxide is a relatively new technique for extracting volatile oil and oleoresin. The peculiar turmeric aroma is imparted by ar-turmerone, the major aroma principle in the oil. 

Rupe et al. (1934) could identify two major ketonic sesquiterpenes - ar-turmerone and turmerone (C15H20O, C15H220) - responsible for the aroma of turmeric. In addition, p-cymene, P-sesquiphellandrene and sesquiterpene alcohols have also been reported (Malingre, 1975). 

The ratio of turmerone to ar-turmerone as reported by Rupe et al. (1934) is 60 40, while analysis of the volatile oils from commercial oleoresin shows a ratio of 80 20 (Salzer, 1977). The physico-chemical properties of turmerone and ar-turmerone are given in Table 6.3. The effect of maturity on the major components of rhizome oil from turmeric grown in Sri Lanka also indicated ar-turmerone (24.7-48.9%) and turmerone (20-39%) as the major compounds (Cooray et al., 1988 Nigam and Ahmed, 1991). Golding et al. (1982) demonstrated the... 

GC-MS analysis of rhizome oils from five different Curcuma species shows variations in the major components, e.g. ar-turmerone (2.6-70.3%), a-turmerone (trace 6.2%) and zingiberene (trace-36.8%). Li et al. (1997) analysed a series of oils produced from several Zingiberaceae plants, including the rhizome oil of turmeric, using GC-MS. Thirty-five components were identified and turmerone (49%), ar-curcumene (15%) and ar-turmerone (6.4%) were the major compounds. 

Separation and purification of three turmerones, e.g. ar-turmerone, a- and P-turmerone, from turmeric oil extracted by supercritical carbon dioxide gave 71% purify by weight. Subsequently, purification using a normal-phase silica gel 60 column could separate and purify three major turmerones with 86% purify by weight of ar-turmerone and 81% purity by weight of a- and P-turmerone. These were identified by liquid-solid chromatography, NMR qualification and HPLC quantification, respectively (Li-Hsun Chang et al., 2006). 

Table 6.3. Physico-chemical properties of turmerone and ar-turmerone.

The composition of essential oil extracted using SC-C02 has been compared with that of steam-distilled oil by GC-MS (Gopalan et al., 2000b). Out of the 21 components identified, ar-turmerone and turmerone constituted about 60% of the total oil. Analysis of the cyclohexane extract of turmeric by GC-MS coupled with Pseudo Sadtler retention indices reveals a series of saturated and unsaturated fatty acids, along with sesquiterpenes. The fatty acids reported are tetradecanoic... 

Comment on the role of sulfur in the steps in this synthesis of the turmeric flavour compound ar-turmerone. 

New syntheses of ( )-ar-turmerone (79) and ( )-nuciferal (80) have been reported (Schemes 10 and 11 ) whereas Meyers and Smith have used the (+)-oxazoline (81) to good effect in an asymmetrically induced synthesis of (+)-ar-turmerone (82) (Scheme 12). A neat one-pot synthesis of /3-curcumene (83) has been developed which involves only two steps (Scheme 13). In a synthesis of the aromatic analogue, (-)-a-curcumene (84), Kumada et al. have used an asymmetrically induced cross-coupling Grignard reaction in the presence of a nickel complex of (85) to produce (84) in 66% enantiomeric excess (Scheme 14). A Vilsmeier-Haack-Arnold formylation of (-f-)-limonene has been used as... 

Arenediazo cyanides, 127 Arenediazonium tetrafluoroborates, 127 Arenesulfonylhydrazones, 243-244 Aristolene, 440 Aromatization, 389 Ar-turmerone, 313, 521 Arylacetylenes, 309 Aryl cyanation, 423 /3-Arylcyclopcntanones, 124 Aryl diazonium salts, 465... 

The sequence has been used for synthesis of natural (+)-ar-turmerone (10), an aromatic sesquiterpene. Reaction of 3 (R = CH3) with p-tolyllithium followed by hydrolysis resulted in 8 in 98.8% enantiomeric purity, although in rather low yield ( 25%). The acid was converted into 10 in essentially 100% ee. ... 

The last example formulates a two step synthesis of ar-turmerone from mesityl oxide. 

The dithioacetal is hydrolysed (mechanism like that on p. 1255), silver and cadmium being instead of mercury (not much gain in environmental friendliness there ), and the double be -moves into conjugation with the resulting ketone to complete the synthesis of ar-turmerone cart out at Caen by A. Thuillier and group, /. Org. Chem., 1979, 44, 2807. 

Lewis acid catalyzed alkylations of cross-conjugated silyl dienol ethers provide routes to a -alkylated ketones. A short synthesis of the sesquiterpene ( )-ar-turmerone has been accomplished using the cross-conjugated TMS dienol ether of mesityl oxide (equation 9). ... 

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