I menthol

Die optische Ausbeute erreicht im ersten Falle Werte bis 55,7 %. Fiir die zweite Reaktion leiten die Autoren die absolute Konfiguration des End-produktes aus der der eingesetzten HiIfsalkohole (i )(—)-Octanol-(2) und (i ) —)-Menthol mit Hilfe des oben formulierten Prelog -Modells und weiterer mechanistischer Uberlegungen her. 

The Rh-BINAP-catalyzed process from myrcene to i-(-)-menthol includes a chiral isomerization and ratios of desirable (-)-isopulegol to other isopulegol isomers of 99.7 0.3 as well as space-time yields of 10 kmol enamine (mol Rh) 1 d-1, and total turnover numbers of 400 000. 

This is the second major commercial route to i-(-)-menthol and the largest application of homogeneous asymmetric catalysis. Yearly, about 15001 (-)-menthol and other terpenes are produced by this route. The space-time yield could be improved to about 8000 mol enamine (mol Rh)-1 in 18 h. The total turnover number (TTN) was improved to an impressive 400 000. 

Crude i-menthol is, obtained similarly from the strongly levorotatory fractions of the ester. It may be purified by esterification with d-menthoxyacetyl chloride and crystallization of the resulting mixture of esters. The i-alcohol-d-acid ester is then readily purified since it is the less soluble and also the more abundant component. Various other methods for purifying the partially active 1-menthol also may be used if desired. See references in Table III, p. 408). 

It was noted that I-menthol could induce CD in the n- ir transition of a large number of saturated, achiral, compounds containing a ketone group when these were co-dissolved in a suitable solvent [12,13]. It was concluded in these works that 1 1 association complexes were formed in the solutions, primarily owing to hydrogen-bonding forces between the two... 

Sulfinate esters, like sulfoxides, are chiral at sulfur and, if the ester is formed from a chiral alcohol i (menthol is best), they can be separated into two diastereoisomers by crystallization—this is really a j resolution of the type you first met in Chapter 16. Attack by the Grignard reagent takes place with i inversion of configuration at sulfur, giving a single enantiomer of the sulfoxide. i... 

Frankland and Price were the first to attempt the resolution of alcohols (and adds) by fractional crystallization of their solid esters. The isomeric solid esters formed from Z-s-butylcarbinol and di-dibenzoyl-glyceric acid failed to separate on crystallization the correspondinjg di-alcohol-i-add ester was liquid. Marckwald and McKenzie effected partial resolutions of di-mandelic add and related adds with i-menthol and d-bomeol, and of di-2-octanol with d-tartaric add, but did not develop a satisfactory method for resolving alcohols. Later investigators, however, have employed the following resolving agents in several more or less successful resolutions of certain alcohols (a) i-menthyl isocyanate, (b) d-camphoric add, (c) d- or i-mandelic add, (d) d- or... 

A stereoselective synthesis of 1-methoxyspiroindoline phytoalexin 63 has been disclosed (14TA1221). Bromine-mediated spirocyclization of 1-methoxybrassinin 60 in the presence of (-i-)-menthol as the chiral auxiliary gives 1-methoxyspirobrassinol menthyl ether 62 in good yield. Subsequent oxidation with PCC under microwave irradiation provides natural (R)-(- -)-l-methoxyspirobrassinin 63 in 68% yield. 

Humans were able to differentiate the odors of the (-I-) and (—) enantiomers of a-pinene, carvone and limonene but failed to differentiate between (-1-)- and (—)-menthol. Both menthol enantiomers have a peppermint odor quality but (—)-menthol has a much stronger cooling effect than (-i-)-menthol [25]. S-(—)-limonene has a turpentine odor impact and R-(-i-)-limonene an orange odor impact [25]. Neomenthol, isomenthol, and neoisomenthol do not present a cooling effect. 

Reaction with Alcohols. Teoc-NT does not react with alcohols in the absence of base however, reaction with benzyl alcohol in the presence of EtsN proceeds quickly to give highly pure (>99%) carbonate in 92% yield after aqueous workup with 5% NaHCOs (eq 1). Even the secondary alcohol ((-i-)-menthol) reacts with Teoc-NT to afford the corresponding carbonate in 97% yield after column chromatography (eq 2). ... 

The principal drawback of this approach is the generation of a 2 1 mixture of diastereoisomeric lactams III-61, which were separated by MPLC. Lactams III-61 were isolated after the reaction of pyroglutamic acid with (-i-)-menthol, anodic oxidation, and treatment of the correspondening methoxylethers amide with allyltrimethylsilane and titanium tetrachloride (Scheme 4.35) [164, 165]. 

Menthyl vinyl ether polymers of the diastereomer-ic menthols (-I-)-menthol, (-1-)-isomenthol and (-I-)-neomenthol have been synthesized and studied. While the menthyl and the neomenthyl derivatives both showed enhanced VCD features compared to the... 

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