P-Menth-l-ene

Manganese(lll) acetate oxidation of (+)-p-menth-l-ene yields the two lactones (165 X=0, Y = CH2) and (165 X = CH2, Y = O) as major products together with anticipated acetates similar oxidation of (+)-pulegone yields the C-2 acetates in low yield and oxidation of isomenthone in the presence of isopropenyl acetate results in acetonylation at C-2 and C-4. Further examples of the rearrangement of epoxides with KOBu -aprotic solvents (pyridine is favoured) have been reported (c/. Vol. 6, p. 44), e.g. (166) to (167), although with the corresponding 1,2-epoxy-... 

Manganese(lil) acetate oxidation of a-pinene yields two lactones analogous to those reported earlier with (+)-p-menth-l-ene however, the major product consists of derived acetates [of a-terpineol, c/5-pin-3-en-2-ol, and myrtenol (224 ... 

Electrochemical reduction of the ozonization products from monoterpenes, i.e., />-meth-l-ene, (-l-)-limonene, (+ )-a// /ia-pinene, (+)-car-3-ene, provides the corresponding double-bond cleavage products in 45-70% yields57. The electrolysis of the acetyloxy hydroperoxide 28 derived from p-menth-l-ene 27 is carried out in an Ac0H/H20(6/1 v/v)— AcONa— (Pb/Pb) system at —1.1 to —1.4V vs. SCE, 2.0 to 2.2 A/dm2 in a divided cell to give the corresponding keto-alcohol 29 in 70% yield (Scheme 3-10). 

Hydrogenation of thymoquinone (170) gives two of the menthane-2,5-diols [(171) and (172)]. All the diastereoisomeric 2,5-diols having the same chirality of the isopropyl group as ( —)-a-phellandrene (173) have been prepared, together with the four p-menth-l-ene-3,6-diols and the two (+ )-p-menthane-2,5-diones, and their interrelations and stereochemistries have been examined. 

Figure 5.1a (Continued) octadiene-3,6-diol) (11) hydroxycitronellol (3,7-di methyloctane-l,7-diol) (12) 8-hydroxydihydrolinalool (2,6-dimethyl-7-octene-l,6-diol) (13) 7-hydroxygeraniol (E-3,6-dimethyl-2-octene-l,7-diol) (14) 7-hydro-xynerol (Z-3,6-dimethyl-2-octene-l, 7-diol) (15) cis and trans 8-hydroxy linalool (E- and Z-2,6-dimethyl-2,7-octadiene-l,6-diol) (16) p-menthenediol I (p-menth-l-ene-7,8-diol) (17) E-geranic acid (3,7-dimethyl-2,6-octadienoic acid) (18) E-2,6-dimethyl-6-hydroxyocta-2,7-dienoic acid (19) E- and Z-sobrerol or p-menthenediol II (p-menth-l-ene-6,8-diol) (20) cis and trans rose oxide (21) nerol oxide (22) 2-exo-hydroxy-1,8-cineol (23) 1,8-cineol (24) wine lactone (25) cis and trans 1,8-terpin (26) triol (2,6-dimethyloctane-2,3,6-triol) (27) hotrienol [(5E)-3,5-dimethylocta-l,5,7-trien-3-ol] (28) myrcenol (2-methyl-6-methylene-7-octen-2-ol)...

Reactions. Grignard reaction and hydrogenation of the appropriate methyl aryl ketone yielded isothymol.877 Carvacrol was formed in excellent (83%) yield on heating p-menth-l-ene oxide with Pd.878 Aromatic aldehydes can beprotected in situ by formation of a-aminoalkoxides and their O-trimethylsilyl ethers thus 4-formyl-benzoic acid could be protected and elaborated (Grignard reaction) into (264).879... 

In minor amounts ( <10 %) the corresponding (Z)-iso-mer, 2-vinyl-2-methyl-tetrahydrofuran-5-one, the four isomeric linalool oxides in their furanoid and pyrano-id forms, the isomeric acetates of pyranoid linalool oxides as well as 3,9-epoxy-p-menth-l-ene were identified as linalool metabolization products. Quantitative variations depending on the B cinerea strain used were observed. 

These fungal conversion products comprised (E)- (19) and (Z)-2,6-di-methyl-2,7-octadiene-l,6-diol (20), the furanoid (Z)- (21) and (E)-linalool oxides (22), the pyranoid (Z)- (23) and (E)-linalool oxides (24), their isomeric acetates (25) and (26), 3,9-epoxy-p-menth-l-ene (27) and 2-vinyl-2-methyl-tetrahydrofuran-5-one (28). 

Finally, let us consider the by-products of linalool transformation by I3 cinerea. The formation of 3,9-epoxy-p-menth-l-ene (27), the character impact compound of fresh dill herb (14), can be understood by allylic rearrangement of (E)-2,6-dimethyl-2,7-octadiene-1,6-diol (19) to the corresponding hydroxygeraniol (-nerol). This compound is known to undergo cyclization to the epoxy derivative (27) under acidic conditions (15). 

The "right half of the sesquiterpene (+)-p-selinene (as drawn below) includes (R)-(+)-limonene as a substructure. Retrosynthetic disconnection to (if)-(+)-limonene leads to the intermediate carbenium ions la and lb via 15-nor-ll-eudesmen-4-one (carbonyl alkenylation) and 15-nor-13-chloro-2-eudesmen-4-one (dehydrogenation, protective masking of the double bond in the side chain). These carbenium ions arise from (if)-9-chloro-p-menth-l-ene and the acylium ion Ic (synthone) originating from 3-butenoic acid as reagent (synthetic equivalent). (i )-/7-Menth-l-en-9-ol, on its part obtained by hydroboration and oxidation of (if)-(-l-)-limonene, turns out to be the precursor of the chloromenthene. 

As shown in Figure 19.49, S. litura converted (4/ )-p-menth-l-ene (62) at C-7 position to (47 )-phellandric acid (65) (Miyazawa et al, 1996b). On the other hand, when Cladosporium sp. Ti was cultivated with (+)-limonene (68) as the sole carbon source, it converted 62 to trans-p-menthane-l,2-diol (54) (Mukherjee et al, 1973). 

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