S- -Citronellol

Ru(II)-BINAP complexes (1) can effect enantioselective hydrogenation of pro-chiral ally lie and homoallylic alcohols, without hydrogenation of other double bonds in the same substrate.1 The alcohols geraniol (2) and nerol (3) can be reduced to either (R)- or (S)-citronellol (4) by choice of either (R)- or (S)-l. Thus the stereochemical outcome depends on the geometry of the double bond and the chirality... 

ASYMMETRIC HYDROGENATION OF ALLYLIC ALCOHOLS USING BINAP-RUTHENIUM COMPLEXES (S)-(-)-CITRONELLOL (6-Octen-1-ol, 3,7-dimethyl, (S)-)... 

Crude BINAP-Ru complex with consistent spectral characteristics can be used for hydrogenation of geraniol (98.7% pure commercial geraniol containing 1.3% of nerol, distilled from 4 A molecular sieves, 4.7 M substrate in 95% aqueous methanol, 2.8 mM Ru(OCOCH3)2[(R)-BINAP], 100 atm of H2, 20°C, 8 hr), to give (S)-citronellol in 96% ee, 97% isolated yield. 

With a commercially available 98.7 1.3 mixture of geraniol and nerol as substrate, (S)-citronellol in 96% ee is obtained. See also Note 7. 

S)-(-)-CITRONELLOL from geraniol. An asymmetrically catalyzed Diels-Alder reaction is used to prepare (1 R)-1,3,4-TRIMETHYL-3-C YCLOHEXENE-1 -CARBOXALDEHYDE with an (acyloxy)borane complex derived from L-(+)-tartaric acid as the catalyst. A high-yield procedure for the rearrangement of epoxides to carbonyl compounds catalyzed by METHYLALUMINUM BIS(4-BROMO-2,6-DI-tert-BUTYLPHENOXIDE) is demonstrated with a preparation of DIPHENYL-ACETALDEHYDE from stilbene oxide. A palladium/copper catalyst system is used to prepare (Z)-2-BROMO-5-(TRIMETHYLSILYL)-2-PENTEN-4-YNOIC ACID ETHYL ESTER. The coupling of vinyl and aryl halides with acetylenes is a powerful carbon-carbon bond-forming reaction, particularly valuable for the construction of such enyne systems. 

B. (S)-(-)-Citronellol. Geraniol (12.9 mL, 74 mmol) (Note 14) and 95% methanol (15 mL) (Note 15) are placed in a dry, 80-mL Schlenk tube and the mixture is degassed by five freeze-thaw cycles. Another dry, 80-mL Schlenk tube, equipped with a rubber septum and a magnetic stirring bar and filled with argon, is charged with Ru(OCOCH3)2[(R)-BINAP] (45 mg, 53 pmol) (Note 16). The system is evacuated and... 

The procedure for the synthesis of the title compound is a representative example of asymmetric hydrogenation in the presence of BINAP-Ru(ll) diacetate.5 The method is based on the synthesis of BINAP-Ru(ll) dicarboxylate complexes and enantioselective hydrogenation of geraniol.7 The present method provides the first practical means for asymmetric synthesis of (S)- and (R)-citronellol. (S)-(-)-Citronellol of optical purity up to 92% can be obtained in a limited quantity from rose oil. A microbiological reduction of geraniol was reported to give enantiomerically pure (R)-(+)-citronellol. ... 

R,S)-Citronellal can be purchased from BASF, and (R)-citronellal from Dragoco, Fluka, or Takasgo Perfumery Co., Ltd., Japan. (R)-Citronellal can also be synthesized from pulegone with ee >99%.5 (S)-Citronellal may be obtained by oxidation of (S)-citronellol,6 which is accessible by different routes with ee 95%.7 The optical purity of citronellal can be determined by GLC after conversion to the acetal of (-)-(2R,4R)-pentanediol.8 For the reactions described, (R,S)-citronellal from BASF, (R)-citronellal from Dragoco, and (S)-citronellol from Fluka were used. (R,S)-Citronellal... 

Chiral crotonates derived from S-citronellol, l-(—)-menthol, and 5-solketol undergo 1,3-dipolar cycloaddition with cyclic and acyclic nitrones.66 Asymmetric 1,3-dipolar cycloaddition of optically active trifluoromethylated a, /i-unsaturated aryl sulfones (43) with nitrones yield the corresponding isoxazolidines (44) and (45) with high regio- and... 

For field applications, we normally use component XV as a mixture with its biologically less active stereoisomers. Our most practical route (Figure 7) to material suitable for commercial use produces a mixture which is only partially enriched in the J5 isomer at C-3 (52 see also 53). Commercially available (S)-(-)-citronellol of moderate optical purity (ca. 75% enantiomeric excess 54) is used as the starting material. The copper(I) catalyzed addition of 3-butenylmagnesium chloride to 6,7-epoxy-... 

Rose (Morocco) Rose (Bulgaria, Turkey) Rosa centiofolia Rosa damascena (S)-Citronellol, geraniol, nerol (23), 2-phenylethanol, (4R)-rose oxide (24), /3-damascone (25), /3-damascenone (26) 95,96... 

Geranium Pelargonium graveolens (S)-Citronellol, geraniol, (4S)-rose oxide 95,96... 

Similarly, catalytic hydrogenation of geraniol (1.60) in the presence of Ru-(i )-BINAP complex yields (S)-(—)-citronellol (1.61) in high yield . ... 

Torii has reported the electrochemical oxyselenation-deselenation of alkenes to give allylically rearranged allyloxy products. A typical example is given below (equation 23).Benzyl- or acetyl-(S)-citronellol was mixed in acetonitrile/water solution with diphenyl diselenide (0.5 mol equiv.) and a catalytic amount of tetraethylammonium bromide, and was electrolyzed at room temperature in an undivided cell using platinum electrodes and a constant current density of 10 mA cm. The corresponding allylic alcohols were isolated in excellent yields. In methanolic solution, using a reduced amount of diphenyl diselenide (20 mol %), the methoxy compounds were obtained in slightly reduced yields. 

In the diterpene series a notable recent example of semisynthesis is that (ref.24) of pachiclavularolide (28) a substance isolated from the soft coral, Pachiclavularia violacea. starting from S-citronellal readily available from S-citronellol. The key step in the formation of the macrocycle is an intramolecular palladium-catalysed diyne cyclisation following initially a Mislow-Evans rearrangement of a sulphinyl ester from S-citronellal. ... 

Oppolzer has developed a method of asymmetric synthesis based on the use of the chiral auxiliaries 39A and 39B derived respectively from (+ )-camphor [(+ )-40] and (- )-camphor [(- )-40]. Crotonylation of 39A gave the ester that was attacked by 4-methyl-3-pentenyllithium in the presence of copper iodide tributylphosphine and boron trifluoride from only one side of the molecule, the product 41 having the (S)-configuration (enantioselectivity 98.5%). The ester 42—similarly obtainable from 39B—was methylated under similar conditions, also yielding 41 with 92% enantioselectivity. (S)-Citronellic acid [(S)-36] or (S)-citronellol [(S)-33] were then obtained from 41 by the action of sodium hydroxide or lithium aluminum hydride (Scheme 6). Reduction of potassium... 

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