Reduction, double

With both building blocks 103 and 109 in hand, the total synthesis of lb was completed as shown in Scheme 17. Coupling of acid 103 and alcohol 109 under Yamaguchi conditions to give ester 110 and subsequent desilylation followed by chemoselective oxidation provided hydroxy acid 111. Lactonization of the 2-thiopyridyl ester derived from 111 in the presence of cupric bromide produced the macrodiolide 112 in 62% yield, which was finally converted to pamamycin-607 (lb) via one-pot azide reduction/double reductive AT-methylation. In summary, 36 steps were necessary to accomplish the synthesis of lb from alcohols 88 and 104, sulfone 91, ketone 93, and iodide rac-97. 

Reactions of different organometallic species with thiocarbonyi compounds have been extensively investigated and been shown to proceed both in a carbophilic and a thiophilic fashion. However, other reactions can be observed simultaneously such as reduction, double addition, coupling, deprotonation and formation of enesulfides1,226,423. A complex pattern appears in the reactions of thioketones with lithium or Grignard reagents424. The first application of Reformatsky reagents in C—C bond formation by reaction with... 

The above reactions take place in the presence of an organic tertiary amine as base, but in the presence of calcium hydroxide reductive double carbonylation takes place with the formation of ct-hydroxy acids (equation 64). ° To maximize the yield of hydroxy acid it is necessary to use isopropyl alcohol as... 

Reductions, Double bonds of the styrene-CrfCOlj complexes are selectively saturated with Sml2 in the presence of water. ... 

Additional metabolic reactions that have been attributed to the intestinal flora are dehy-droxylations (alcoholic), decarboxylations, O-demethylations, nitro reductions, double bond reductions, azo reductions, scission of heterocyclic ring systems, and even aromati-zation of cyclohexyl carboxylic acids. 

Intramolecular tandem Michael addition-amide formation in the intermediate (291) afforded an epilupinine precursor (Scheme 60) <89H(29)1209>. Another quinolizidine synthesis forming two a bonds in its key step is the reductive double alkylation of azido epoxides with an (o leaving group (292). This strategy has been applied to the synthesis of ring-expanded analogues of indolizidine alkaloids (e.g. (293)) from D-arabinose (Scheme 61) <93TL822l>. 

The electrochemistry of [Th(Por)(OH)2]3 (Por=OEP,TPP) is of particular interest as they contain three redox active metalloporphyrin units (Kadish et al. 1988). The cyclic voltammogram of the OEP complex recorded in THE at -72 C shows three reversible one-electron reduction couples at -1.49, -1.70, and -1.87 V vs. SCE. As the temperature rises to room temperature, the third reduction becomes irreversible, and it has been shown that it involves a one-electron transfer followed by a fast chemical reaction (probably dissociation) and an additional one or more electron reduction (an electrochemical ECE-type mechanism). The UV-Vis spectrum of the electroreduced species [Th(OEP)(OH)2]3 shows absorption bands at 411, 456, and 799 nm, and its ESR spectrum displays a signal at g=2.003, both of which are characteristic of a porphyrin ti radical anion. Further one-electron reduction doubles the molar absorptivities of the absorption bands at 456 and 799 nm, indicating that the second reduction is also based on porphyrin. The TPP analog [Th(TPP)(OH)2]3 also exhibits three reversible one-electron reductions at -1.13, -1.27, and -1.36V at -55 C, which are shifted by 360-510mV relative to the respective processes for [Th(OEP)(OH)2]3 at —72 C. Three additional irreversible reductions at —1.76, -2.00, and —2.10 V are also observed for this complex when the potential is scanned to -2.20 V which may be due to the formation of dianions localized on each of the three porphyrin units. Spectroelectrochemical data also indicate that the initial three reductions occur at porphyrin based orbitals. 

Nickel triethylamine A 8.9-Octahydro-7-quinolones by reductive double ring closure... 

Scheme 9.25 Synthesis of endiandric acid A by domino reduction/double electrocyclization.

Typically, the anode consists of small particles of hydride-building alloy held together by a binder and conductive additive (acetylene black) and pressed onto a Ni-foam current collector. The impedance of the particle surface is determined by the charge transfer resistance of hydrogen reduction, double layer capacitance, and the impedance of subsequent solid-state diffusion into the bulk of the particle. To take into account electronic resistance between the particles and ionic resistance of electrolyte in pores, as well as the impedance of the particle surface, we can use the transmission line model of Figure 4.5.9. Because particle shape is best approximated as a sphere, diffusion with spherical boundary conditions, as in Eq. (30) can be used for Za. 

Asymmetric reduction, double bond isomerisation and hydroboration... 

Yamaguchi S, Xu C, Tamao K (2003) Bis-silicon-bridged stilbene homologues synthesized by new intramolecular reductive double cyclization. J Am Chem Soc 125 13662-13663... 

Ultimate tensile Tensfle yield Elongation Reduction Double shear ... 

Simple but still very interesting transformations are the reductive double bond shift (197 198) [87] and the conversion of primary amines into optical active... 

Palladium-carbon/acetic acid Stereospecific reductive double ring closure to N-condensed heterocyclics... 

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