Y>-Cymene

Dehydrogenation ofy -menthadienes and a-piuene ia the vapor phase over catalysts such as chromia—alumina produces y -cymene (70). / -Menthadienes can be disproportionated over a Cu—Ni catalyst to give a mixture of yvmenthane andy -cymene (71). 

Figure 3.10 Reagents and conditions (i) ligand 17, [Ru(>y-cymene)Cl2]2, HCOOH/EtsN, CH2CI2, 98 % (ii) BH3 Me2S, THE, 92% (iii) methyl chloroformate, K2CO3, CH2CI2 then LiAlH4, THF, two steps 92% (iv) NaH, 4-chlorohenzotrifluoride, DMSO, then saturated HCl of Et20, 90%. Reprinted from reference [3], with permission from Elsevier.

Although the cyclometallated ruthenium complexes were formerly claimed to be configurationally stable at the stereogenic metal, Brunner and co-workers have shown that they are indeed configurationally labile. Revisiting previous NMR spectroscopic data, variable-temperature NMR studies (—80 to 21 °G) were carried out, and showed that epimerization processes take place. This has also been assessed by the isolation of cyclometallated ruthenium and osmium derivatives which have been synthesized through transmetallation reactions of [ MGl(p-Gl)(77 -y>-cymene) 2] (M = Ru, Os) with the enantiomerically pure mercurated (3 )-(-h)-iV,iV-dimethyl(l-phenyl)ethyl-amine. In both cases, two diastereoisomers (i M c) ( m c) were obtained, which undergo epimerization in... 

Gymene. Methyhsopropylben2ene [25155-15-1] can be produced over a number of different acid catalysts by alkylation of toluene with propylene (63—66). Although the demand for cymene is much lower than for cumene, one commercial plant was started up in 1987 at the Yan Shan Petrochemical Company in the People s RepubHc of China. The operation of this plant is based on SPA technology offered by UOP for cumene. The cymene is an intermediate for the production of y -cresol (3-methylphenol) [108-59-4]. 

Tne oil thus tnvited vea a cooameruiivl peld of 00 3 per ceut. of thymol of a perf<.-ct)y white crystslliue character. Carvacrol it also probably reseut in the oil, as well as cymene, and traces o d-HmonenP.. 

Hydrazoic acid reaction with cyclobu-tanecarboxyhc acid, 47, 28 Hydrogenation of t butylazidoacetate to glycme ( butyl ester, 46,47 Hydrogen bromide 46, 43 reaction with y butyrolactone, 46, 43 Hydrogen fluoride anhydrous, precautions in use of, 46, 3 in preparation of mtromum tetra-fluoroborate 47, 57 reaction with benzoyl chloride, 46,4 with boron tnfluonde in conversion of p cymene to m cymene, 47, 40 in bromofluorination of 1 heptene, 46, 11... 

Fig. 1. P MAS NMR spectrum of (a)Ru-BrNAP/PTA/y-Al203, and (b)Ru-BINAP crt rlex In order to find the characteristics of the immobilized catalyst, asymmetric hydrogenation of the prochiral C=C bond was performed as a model reaction. Firstly, three different homogeneous Ru-BINAP complexes including [RuCl2((R)-BINAP)], [RuCl((R)-BINAP)(p-cymene)]Cl and [RuCl((R)-BINAP)(Benzene)]Cl were immobilized on the PTA-modified alumina. Reaction test of immobilized catalysts showed that [RuCl2((R)-BINAP)] was the most active and selective so all the experiment were done using this catalyst afterwards.

Lun, R., Varhanickova, D., Shiu, W.-Y., Mackay, D. (1997) Aqueous solubilities and octanol-water partition coefficients of cymenes and chlorocymenes. J. Chem. Eng. Data 42, 951-953. 

Recently, Yu and co-workers developed an operationally simple catalytic system based on [RuCl2(/>-cymene)]2 for stereoselective cyclization of a-diazoacetamides by intramolecular carbenoid C-H insertion.192 /3-Lactams were produced in excellent yields and >99% m-stereoselectivity (Equation (53)). The Ru-catalyzed reactions can be performed without the need for slow addition of diazo compounds and inert atmosphere. With a-diazoanilide as a substrate, the carbenoid insertion was directed selectively to an aromatic C-H bond leading to y-lactam formation (Equation (54)). 

Aqueous two-phase hydrogenations are dominated by platinum group metal catalysts containing water-soluble tertiary phosphine ligands. The extremely stable and versatile N-heterocyclic carbene complexes attracted only limited interest, despite the fact that such complexes were described in the literature [62-65]. Recently, it was reported that the water-soluble [RuXY(l-butyl-3-methylimi-dazol-2-ylidene) ( 76-p-cymene)]n+ (X=Ch, H20 Y = C1-, H20, pta) complexes preferentially hydrogenated cinnamaldehyde and benzylideneacetone at the C = C double bond (Scheme 38.5) with TOF values of 30 to 60 h 1 in water substrate biphasic mixtures (80 °C, lObar H2) [66]. 

Figure 4. LC separation of a terpene mixture. 1, Thymol 2, p-cymene 3, y-terpinene 4, a-terpinene 5, 3-pinene 6, a-pinene. Column 30 cm x 0.22 mm I.D. 3-ym Spherisorb ODS. Mobile phase methanol-water (80 20) Detection TIC (ions of m/z <40 suppressed).

Aromatic monoterpenes such as p-cymene 9 and its hydroxylated derivatives thymol 12 and its isomer carvacrol 13 always occur along with a-terpinene 23, y-terpinene 25 and terpinen-4-ol 29 (Structure 4.8). Metabolites, likep-cymene-8-0I 30 and cuminyl alcohol 31 may also be derived from p-cymene (Fig. 4.4). 

Origanum oils y-Terpinene, p-cymene, thymol, carvacrol Savoury flavours... 

SELECTIVE REDUCTION OF CARBONYL GROUP IN p,y-UNSATURATED a-KETOESTERS BY TRANSFER HYDROGENATION WITH Ru(P-CYMENE)(TsDPEN)... 

The transfer hydrogenation of a-keto- S -unsaturated esters, catalyzed by Ru(p-cymene)(TsDPEN) (TsDPEN monotosylated l,2-diphenylethylene-l,2-dia-mine) with 2-propanol as the hydrogen source, has been developed as an efficient method for the preparation of a-hydroxy-)S, y-unsaturated esters or acids. 

In conclusion, we have found a convenient and practical method for the selective reduction of C=0 bond of a wide spectrum of a-keto-)S, -unsaturated esters with Ru(p-cymene)(TsDPEN) as catalyst. The transition metal catalyzed transfer hydrogenation reaction with good selectivity and high efficiency offers possibilities to provide the optically active a-hydroxy-/l, y-unsaturated esters with chiral catalysts. Table 3.8 gives different substrates that can be reduced with Ru(p-cymene) (TsDPEN) complex in isopropyl alcohol. 

Juniperus rigida Sieb. et Zucc. J. rigida Sieb. et Zucc. f. modesta (Nakai) Y. C. Chu Tu Soon (Juniper) (fruit) Alpha-pinene, myrcene, carene, limonene, p-cymene, beta-elemene, caryophyllene, humulene, bomeol, r-cadinene, terpinene, citronellol, anethole.48 Hemorrhage, treat hemoptysis, inflammation, kidney infection, arthritis joint infection. 

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