Alkenone

Treatment of the Z-aldehyde 9 (R1 = R2 = H) with trifluoroacetic acid in dichloromethane at — 10 C, then with l,4-diazabicyclo[2.2.2]octane or /V,/V-diethylpyridin-4-amine, constitutes the first synthesis of 27/-azepine (10, R1 = R2 = H) which was isolated, with great difficulty and in very low yield (1 %), as a highly volatile, unstable oil, the structure of which was confirmed by high field H and 13CNMR spectroscopy.290 Similar treatment of the Z-alkenones 9a-d furnishes the thermally unstable (5)-2/7-azepines lOa-d in much higher yields.291... 

Remarkable cis diastereoselectivity occurs in the addition of l-alkoxy-l-(trialkylsilyloxy)-ethenes to y-silyloxy-substituted cyclo-2-alkenones using mercury(II) iodide as a catalyst265,266. C-C Bond formation syn to the electron-withdrawing silyloxy substituent has been attributed to the stabilization of the emerging cr -orbital at the -carbon by interaction with the ct(CH) bond at the y-carbon atom267. 

An interesting new method for the conversion of [I, y-epoxy sulfones (82) to cyclo-alkenones (85) has been developed61. It includes the addition of alkyllithium to y-hydroxy-a,/ -unsaturated sulfones generated from 82 and the alkylation of sulfonyl carbanion thus formed. Oxidation of the resulting y-hydroxy sulfone to 84 followed by elimination of benzenesulfinic acid gives the desired product 85 in good yields (equation 72)61. 

Alkenones were used by Rao and coworkers [40] to prepare cyclohexane derivatives which, for example, can be transformed into substituted arenes in a single step. Another interesting intermolecular Michael/intramolecular aldol reaction sequence for the construction of the highly substituted 2-hydroxybicy-clo[3.2.1]octan-8-one framework has been described by Rodriguez group [41]. This process can be extended to a three- and even a fourfold domino reaction [41a, 42, 43],... 

Pagani, M. (2002) The alkenone C02 proxy and ancient atmospheric carbon dioxide. Philosophical Transactions of the Royal Society of London, Series A 360, 609 632. 

A new formal synthesis of ( )-zizaene (136) via the fragmentation reaction is a typical example 45,46). When the enol acetate (132) was irradiated, the isolable photoadduct (133) was formed together with other isomers. Reduction and mesylation of which afforded the mesylate (134). Then, fragmentation reaction would yield an epimeric mixture of the alkenone (755) in the presence of NaOH in aqueous dioxane at 60 °C, thus formulated a total synthesis of (+)-zizaene (136) 45-46). 

The biomimetic protocol was invented by Julia and Colonna, and involves the use of polyamino acids (such as poly-(L)-leucine) as the catalysts for peroxide oxidation of chalcones, styryl alkyl ketones and conjugated alkenones. The substrate range is broad, especially when using immobilized catalysts and an organic solvent containing the substrate, urea-hydrogen peroxide and an organic base (Scheme 22)[101]. 

The haptophyte microalga Emiliania huxleyi produces biomarkers in the form of long-chain (C37, C38, and C39) alkenones (Brassell, 1993). Alkenones are well preserved in marine sediments and their molecular distributions and isotopic composition have been used to infer paleo-temperatures (Brassell, 1993) and pC022 values (Jasper et ak, 1994), respectively. Unsaturation patterns in the alkenone series are related to the growth temperature of the haptophyte algae that produce these compounds (Brassell et ak, 1986 Prahl and Wakeham, 1987), and hold great promise as indicators of absolute ocean paleotemperature. 

Laws, E.A., B.N. Popp, R.R. Bidigare, U. Riesbesell, S. Burkhardt, and S.G. Wakeham. 2001. Controls on the molecular distribution and carbon isotopic composition of alkenones in certain haptophyte algae. Geochemistry Geophysics Geosystems January 25, 2001. 

Alkenones Long-chain, unsaturated ketones that are synthesized exclusively by certain haptophyte microalgae (e.g., Emiliania huxleyi). 

Examples of common long-chain alkenones found in marine sediments. Me = methyl Et= ethyl. 

In the non-cyclic alkenone series, regiosdectivity in the hydrodimerization step is not well controlled. Dissolving metal reducing agents such as sodium amalgam,... 

Furthermore, electrochemical oxidation with TEMPO mediated aromatization of 6-membered cyclic dienes" and transformation of alkenes to alkenones also took place" . 

From the literature several examples of the nonenzymatic chemo- and enantiose-lective reduction of the carbonyl group of (E)-alkenones are known [46], but no example has been published for the similar reduction of a (Z)-methylalkenone... 

As depicted in Table 2.2.7.2, a,P-unsaturated alkenones possessing the Z configuration are only poorly accepted by the enzymes tested. In addition, with these substrates only low enantioselectivity was observed for the reduction step. 

The enzymatic reduction of T-configured alkenones represents a valuable alternative to the enzyme-catalyzed reduction of the corresponding alkynone with subsequent partial reduction of the C-C triple bond. Nevertheless, since in our results the Z-configured vinylic alcohols are not accessible in enantiopure form by enzyme-catalyzed reduction of the olefinic ketones, for this class of compounds the two-step process via the propargylic alcohols is a highly valuable new strategy. 

Cyclic terpene aldehydes occur in essential oils only in low concentration. These aldehydes are seldom used as single fragrance substances. A few of the cyclic terpene ketones are commercially important as fragrance and flavor substances, for example, menthone and carvone, which have the / -menthane skeleton, and the ionones, which have a (trimethylcyclohexenyl)alkenone skeleton. The ionones and... 

On ultraviolet irradiation of bicyclo[2.2.1]hept-5-en-2-one in diethyl ether for 1 hour, the rearrangement product bicyclo[3.2.0]hept-2-en-7-one (33) was formed in 90% yield.103 Other bicyclo[n.m.l]alkenones gave the rearranged cyclobutane products, albeit in lower... 

Sodium toluene dispersion of, 55, 65 Sodium p-toluenesulfinate, 57, 103 Spiro[4 n] alkenones, 58, 62 Spiro[cyclopentane-l,l -indene] 55, 94 Squalene, 56, 116 Squalene, 2,3-epoxy, 56, 116 Stannic chloride, 56, 97 Steroids synthesis, 58, 85 E Stilbene, 55, 115,58, 73 z-Stilbene, 58, 133 Styrene, 56, 35,58, 43 Styrene glycol, 55, 116 Styrene glycol dimesylate, 55, 116 Succinic acid, 58, 85 Succinic anhydride, 58, 85 Sucunimide, 56, 50, 58, 126 Succimmide, Vbromo, 55, 28, 56, 49 SULFIDE CONTRACTION, 55, 127 Sulfide, dimethyl-, 56, 37 SULFIDE SYNTHESIS, 58, 143,58, 138 SULFIDE SYNTHESIS ALKYL ARYL SULFIDES, 58, 143 SULFIDE SYNTHFSIS DIALKYL SULFIDES, 58, 143 SULFIDE SYNTHESIS UNSYMMETRI-CAL DIALKYL DISULFIDES, 58, 147 SULFONYL CYANIDES, 57, 88 Sulfur tetrafluoride, 57, 51... 

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