A- Curcumene

The sesquiterpenoid hydrocarbons (5)-a-curcumene (59) and (5)-xanthorrhizol (60) were prepared by asymmetric conjugate addition of the appropriate aryllithium reagent to unsaturated oxazoline 56 to afford alcohols 57 (66% yield, 96% ee) and 58 (57% yield, 96% ee) upon hydrolysis and reduction. The chiral alcohols were subsequently converted to the desired natural products. ... 

Almost simultaneously with the identification of 2E, 4 , 6Z- 10 COOMe, a thermally unstable stereoisomer, 2E, 4Z, 6Z- 10 COOMe 118, was found to be a key component of the male-produced sex pheromone of Thyanta pallidovirens> along with the sesquiterpenes (+)-a-curcumene, (-)-P-sesquiphellandrene, and (-)-zingiberene 119 [10,25]. 2E, 4Z, 6Z-10 COOMe was an essential component of the attractive blend, whereas any one, any two, or all three of the sesquiterpene components were equally effective as the other portion of the blend. None of the components were active alone. Pheromone blends attracted only females in both laboratory and field bioassays [10]. The same compounds are also produced by the congener T. custator [10] and other Thyanta spp. (J.G. Millar, unpublished data). 

The male produced sex pheromone of the red-shouldered stink bug, Thyantapallidovirens Stal (Hemiptera Pentatomidae), was shown to consist of a blend of methyl ( "2, Z 4,. Z6)-decatrienoate and the sesquiterpenes (+)-a-curcumene, (—)-zingiberene and (—)-P-sesquiphellandrene. In laboratory bioassays, sexually mature males attracted sexually mature females but not males, and females did not attract either sex. Pheromone... 

An example of practical application of the asymmetric cross-coupling, enantioselective synthesis of a-curcumene (19), is shown in Scheme 8F.6 [21]. The compound was synthesized with 66% ee through Ni/(S)-(/ )-PPFA (lOa)-catalyzed cross-coupling of 1 -(p-tolyl)ethylmag-nesium chloride (17) and vinyl bromide (4b). 

Composition of ginger oil prepared from fresh ginger rhizomes was determined by gas chromatography (GC) and GC-MS techniques. The main sesquiterpene hydrocarbons identified were a-zingiberene (27-30%), a-curcumene... 

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... 

This reaction has been extended to a synthesis of a terpene, (R)-a-curcumene (4), in optical purity of 66% in 34% overall yield. The key step is cross-coupling of 2 with vinyl bromide catalyzed by NiClj and 1 to yield optically active 3. ... 

Isopropenyl terpenes. The most convenient synthesis of the natural sesquiterpene ( )-iso-a-curcumene (4) employs the general method of van der Gen (6, 380-381). 

Estradiol bis(trimethylsilyl) ether (235 Scheme 50) has been converted into a diasteromeric mixture of adducts (236) which were hydrolyzed by aqueous acetic acid to a mixture of the isomeric enones (237 36% yield) and (238 9% yield).This provides an especially direct route for the introduction of functionality at C-1, which would otherwise require a multistep sequence. Reductive silylation has also been used to convert anisole into enone (239)which, following a kinetic resolution, has been used in an en-antioselective synthesis of (-i-)-a-curcumene (240 Scheme 51). The silyl substituent was employed to control the stereochemical and regiochemical aspects of subsequent steps. 

Vig et al. have reported the syntheses of y-bisabolene (59) and dehydro-a-curcumene (60). Both isomeric atlantones (61) and (62) have been isolated from Cedrus deodara and a-bisabolol (63) has been isolated from the essential oil of the cotton plant. Two syntheses of nuciferal (64) have been reported by Cast and Naves starting from 2-(p-tolyl)propanal. Russian workers have described the synthesis of Ar-juvabione (67) by alkylation of the )8-keto-ester (65) with (66) followed by hydrolysis, decarboxylation and re-esterification. The isolation and... 

Of the various possible asymmetric cross-coupling reactions, (1) asymmetric alkylation with secondary alkylmetals, (2) asymmetric biaryl synthesis, and (3) asymmetric allylation with allylic electrophiles have been most extensively studied with chiral Ni and Pd complexes [166]. The initial study in this area was reported as early as 1974 by Kumada and his co-workers, but only a meager range of 8-15% ee was reported [167]. By the end of the 1970s, however, the cross-coupling reaction had been sufficiently developed so that its application to the asymmetric synthesis was already practically attractive, as indicated by an asymmetric total sythesis of (R)-(—)-a-curcumene in five steps in 66% ee and 34% overall yield shown in Scheme 1-47 [168]. 

A simple and efficient synthesis of juvabione (58) (c/. Vol. 1, p. 60 Vol. 5, p. 49 Vol. 4, p. 88), a sesquiterpenoid possessing juvenile hormone activity, has been achieved using a combination of hydroboration and carbonylation reactions cf. Scheme 6). A new efficient synthesis of ( )-a-curcumene (59) cf. Vol. 5, p. 51) involves reduction in situ (Li-NHs) of the alkoxide produced from p-tolylmagnesium bromide and 6-methylhept-5-en-2-one. ... 

These lithium derivatives are also well behaved in alkylations and aldol reactions. Krapcho s synthesis15 of the sesquiterpene a-curcumene 92 starts with the chemoselective condensation of... 

The nickel-catalyzed asymmetric cross-coupling between sec-alkyl Grignard reagents with vinyl bromide finds many applications in the synthesis of optically and biologically active substances, e.g. a-curcumene (eq. 2) and 2-aryIpropionic acids, (anti-inflammatory drugs) (eq. 3). ... 

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