Heptenone

Methyl-heptenone from citral (by boiling with solution of carbonate of potassium) 67 5° (4 mm.) 0-8590 1-45611 49-424 49-438... 

Methyl-heptenol is an alcohol with a delicate rose odour, of the formula CgHjgO. It occurs in Mexican and Cayeme linaloe oil, and is-prepared by reducing methyl-heptenone, and has the following characters —... 

Methyl-heptenone, CgH, 0, occurs in various essential oils, especially lemon-grass oil, in which it is associated with, and difi cult to separate from, the aldehyde citral. 

It forms a semi-carbazone melting at 136° to 138°, which can be obtained as follows Ten c.c. of methyl-heptenone are dissolved in 20 c.c. of facial acetic acid, and a mixture of 10 grams of semi-carbazide hydrochloride and 15 grams of sodium acetate dissolved in 20 c.c. of water is added. After half an hour the semi-carbazone is precipitated by the addition of water, and recrystalUsed from dilute alcohol. 

Methyl-heptenone also forms a bromine derivative which is well suited for the identification of the ketone. This body, which has the formula CgHjjBrgO. OH, melts at 98° to 99°, and is obtained as follows Three grams of methyl-heptenone are mixed with a solution containing 3 grams of caustic soda, 12 grams of bromine, and 100 c c. of water. After a time an oily substance is deposited, which is extracted with ether. The solvent is evaporated, and the residue, redissolved in ether, is treated with animal charcoal and filtered. On slow evaporation the product is obtained in well-defined crystals. 

Methyl-heptenone combines with sodium bisulphite. On reduction by means of sodium and alcohol, it forms the corresponding alcohol, methyl-heptenol, CgHj OH, which has the following characters —... 

Ciamician and Silber have found that. light has a marked effect on methyl-heptenone. The ketone was kept in a glass flask, exposed to the light for five months, the flask being exhausted of air, which was replaced by oxygen. When the seal was broken, the contents of the flask were found to be at reduced pressure, and the oxygen was mainly converted into carbon dioxide. 

The methyl-heptenone was decomposed, with the formation of acetone, a ketonic glycol, CgH gOg, and a hydroxydiketone, CgH 402-... 

Methyl heptenone dissolved in 75% alcohol Is reduced with activated aluminum in the presence of methylamine to give isometheptene. 

A comprehensive stereochemical study was carried out concerning the reactions of cyclic enones27. The additions to cyclohexenones and -heptenones containing either a 4-methyl or 5-methyl substituent were studied. Surprisingly, the same selectivity trends were found for the six-membered rings as well as for the conformationally much more complex seven-mcmbercd rings. 

Seven-membered carbocycles are also available from the reaction of alkenylcarbene complexes of chromium and lithium enolates derived from methyl vinyl ketones [79b] (Scheme 65). In this case, the reaction is initiated by the 1,2-addition of the enolate to the carbene complex. Cyclisation induced by a [1,2]-migration of the pentacarbonylchromium group and subsequent elimination of the metal fragment followed by hydrolysis leads to the final cyclo-heptenone derivatives (Scheme 65). 

It is interesting to note that the parent dienone 67 and its 2-methyl derivative 68, when irradiated in strongly acidic media, gave no product which would con espond to the protonated bicyclo[4,l,0]heptenone observed in the photolysis of protonated eucarvone. In FHSO3 at — 66°... 

Just one reaction has been described where lithiated methoxyallene 42 reacted with bicyclo[3.2.0]heptenone 175 to form the triquinane derivative 176 via a tandem oxy-Cope-transannular ring closure sequence (Eq. 8.31) [111]. However, cycloocta-none 177 was isolated as a major product, which is unusual since other alkenyl-lithium compounds and 175 provide only triquinanes. The authors assumed that the additional sp2-hybridized C-atom in the eight-membered ring intermediate (eno-late of 177) induces a conformation which is less susceptible to transannular ring closure. 

Intramolecular [2n + 27r] cycloadditions leading to cyclobutanes formally belong to valence isomerizations. Alkene/alkcne, ketene/alkene, and allene/alkene cycloadditions have received detailed attention. These rearrangements provide powerful methods for the synthetic arsenal. An example is the facile synthesis of bieyelo[3.2.0]heptenones 3 by intramolecular ketene/alkene cycloaddition after electrocyclic ring opening of cyclobutenoncs l.89... 

Methylenecyclopropane undergoes an interesting reaction with cobalt carbonyl com-plexed acetylenes yielding spiro[2.4]heptenone derivatives (equation 19)41. 

Geraniol and citronellal (50-80%), terpenes, methyl-heptenone, bomeol Mineral oils, fatty oils... 

An unexpected, but potentially useful, reaction was discovered during attempts to effect Nef-like transformations of nitrobicyclo[2.2.1]heptenes into bicyclo[2.2.1]heptenones. Thus, treatment of 6-exo-aryl-5-endo-nitrobicyclo[2.2.1 ]hept-2-enes with SnCl2.2H20 in hot THF or dioxane led directly to 3-arylpyridines in moderate yield. 

Worldwide, in excess of five million pounds of linalool and its esters are manufactured for fragrances by five different processes. Three of them involve methylheptenone as an intermediate. The other two are based on turpentine. The three routes to methyl-heptenone are outlined in Figure 13. 

One way in which a small company can keep abreast of new developments is to collaborate with universities. Moreover, such collaboration helps to motivate staff (and publication of results provides advertising). One fruit of such a collaboration was a synthesis of LTB4, in which chiral moieties of the molecule are derived from the enantiomers of a common intermediate (ll).11 Several routes have been devised for enzyme-catalyzed kinetic resolution of bicyclo[3.2.0]heptenones.12 An efficient one that was used for the synthesis of LTB4 (12) is shown in Scheme 29.4. 

Reisinger, A., Koch, R. and Wentrup, C. (1998) Dihydro-1,3-diazepinones and diazabicyclo[3,2.0]heptenones from pyridyl azides. Journal of the Chemical Society, Perkin Transactions 1, (15), 2247-2249. 

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