Alkenones synthesis

Figure 3 Alkenone concentrations ( jLg dry sediment weight) determined over a 2.8 Ma record from ODP Site 1012 off the southern California coast. Note the absence of a down-core decrease in alkenone concentrations that would suggest progressive diagenetic loss of alkenones in older sediments. Evolutionary conservatism in alkenone synthesis is suggested by the stability of the chain length index + X ss)) over the record.

The relationship observed in sediments closely mimics the relation measured between unsaturation in photic zone particulates (Conte et al. in press) and in situ temperature. We should note, however, that the calibration of sedimentary U 7 to mean annual SST represents a statistical relationship and should not be interpreted in too simphstic a manner. We have seen above that this relation holds for sediments because alkenone synthesis generally occurs in the mixed layer, and because alkenone production by selected hapto-phyte algae is less seasonal than many other planktonic groups. Lurthermore, temperatures during the season of maximal alkenone production generally come close to mean annual SST. The index, therefore, is a quite robust proxy for mean annual temperature. It should be kept in mind that regional variations in the factors that control the depth and seasonality of alkenone production can cause the index to deviate from mean annual SST. 

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... 

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). 

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... 

In recent years, most of the attention has focused on the stereocontrolled synthesis of cyclopropanes. The isolation of several structurally intriguing natural product has revived the interest of the scientific community for the development of new methods. Several efficient and practical chiral auxiliaries have been developed for the enantioselective cyclopropanation of olefins. The most efficient chiral auxiliaries have been specifically designed for the cyclopropanation of acyclic allylic alcohols (Table 13.3, entry 1, 2, Protocol 8),24 alkenones,25 cycloalkenones26 (Table 13.3, entry 3,4, Protocol 9), vinyl ethers27 (Table 13.3, entry 5, Protocol 10), and vinylboronate esters28 (Table 13.3,... 

Reactions of trichloromethyl-substituted 1,3-dielectrophiles 551 with hydrazine afforded hydroxy pyrazoles 552 (Equation 111) <2002TL5005>. Cyclocondensation of alkenones 553 with phenylhydrazine under microwave irradiation furnished 5-trichloromethyl-substituted pyrazoles 554 in excellent yields (Equation 112) <2003TL6669>. 4-Alkoxy-l,l,l-trichloro-3-alken-2-ones were useful precursors for the regiospecific synthesis of 5-trichloromethylpyr-azoles using hydrazines <2002SC419, 2002SC1585>. l,l,l-Trifluoro-4-ethoxy-3-buten-2-one, 3-trifluoroacetyl-3-buten-... 

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