Double bonds reduction

FIGURE 25.12 Elongation of fatty acids in mitochondria is initiated by the thiolase reaction. The /3-ketoacyl intermediate thus formed undergoes the same three reactions (in reverse order) that are the basis of /3-oxidation of fatty acids. Reduction of the /3-keto group is followed by dehydration to form a double bond. Reduction of the double bond yields a fatty acyl-CoA that is elongated by two carbons. Note that the reducing coenzyme for the second step is NADH, whereas the reductant for the fourth step is NADPH. 

Horner-Wadsworth-Emmons double bond reduction... 

An indirect method ° of double-bond reduction involves hydrolysis of boranes (prepared by 15-16). Trialkylboranes can be hydrolyzed by refluxing with carboxylic acids,while monoalkylboranes RBH2 can be hydrolyzed with base. ° Triple bonds can be similarly reduced, to cis alkenes. °... 

Substituting deuterium for hydrogen gas in the reduction of BT to DHBT with the catalyst precursor [Rh(NCMe)3(Cp )](BF4)2 has shown that the stereoselective ds-deuteration of the double bond is kinetically controlled by the tj2-C,C coordination of BT. The incorporation of deuterium in the 2- and 3-positions of unreacted substrate and in the 7-position of DHBT has been interpreted in terms of reversible double-bond reduction and arene-ring activation, respectively (Scheme 16.14) [55]. 

Reduction reactions mediated by microorganisms may include the reduction of nitro bonds, sulfoxide reduction, and reductive dehalogenation. Reduction of the nitro group to amine involves the intermediate formation of nitrase and hydroxy amino groups. Selected reductive reactions may involve the saturation of double bonds, reduction of aldehydes to alcohols or ketones to secondary alcohols, or of certain metals. The main reductive processes in the subsurface environment have been discussed earlier in this chapter. 

Successful double-bond reductions are shown in Scheme 36. Formic acid can be used <1970LA(739)32>, although N-formylation may occur <1970M1295>. With the right conditions, sodium cyanoborohydride is also a suitable reagent for dihydrothiazines <1994ACS517> and dihydrothiazin-2-ones <2006SL3259>. 

With an ot, y-ketodiol, cyclization to produce a 3-furanone derivative is feasible, as is shown for the synthesis of ascofuranone (71) and geiparvarin (72) (Scheme 6.57) (286). The precursor for 71 was prepared by the cycloaddition of diene 66 to nitroalcohol 67. In this case, regioselective attack occurred only on the terminal double bond. Reductive cleavage-hydrolysis of the isoxazoline adduct 68 with Mo(CO)6 followed by acid-induced cyclization led to the furanone intermediate (286). A similar strategy was used for the synthesis of geiparvarin (72) (Scheme 6.58) (286). 

An indirect method286 of double-bond reduction involves hydrolysis of boranes (prepared... 

The complete reduction of coal proceeds from aromatic rings through rings containing olefinic double bonds to saturated compounds. While reduction of the benzene ring takes place at a current efficiency of about 80% (8), current efficiency for reducing an olefin (1-decene) is only 27% as shown in this paper. The slow step in the coal reduction may very well be reduction of olefinic double bonds. An increase in the rate of olefinic double bond reduction may therefore lead to a considerable increase in current efficiency. 

An approach to the synthesis of angularly substituted polycyclics through the Diels-Alder cycloaddition of dihydrothiophenes has been devised (69JA7780). The easily prepared 2,5-dihydro-4-methoxycarbonyl-2-thiopheneacetic acid methyl ester (316) was heated at 180 °C with excess butadiene to yield (317). Desulfurization and double bond reduction of the cycloadduct with W-5 Raney nickel gave (318) which was characterized by conversion to the corresponding diacid and comparison with an authentic sample. Dieckmann cyclization of (318) is known to lead to the 5-methyl-1-hydrindanone (319 Scheme 68). The use of other dienes in the [4 + 2] cycloaddition process will, of course, produce more highly functionalized hydrindanones. 

This form of palladium can be used for the hydrogenation of almost any triple bond to the double bond. Reduction of doubly substituted acetylenes gives cis olefins. 

The last sequence of reactions in the biosynthesis of choles-terol involves approximately 20 enzymatic steps, starting with lanosterol. In mammals the major route involves a series of double-bond reductions and demethylations (fig. 20.10). The sequence of reactions involves reduction of the A24 double bond, the oxidation and removal of the 14a methyl group followed by the oxidation and removal of the two methyl groups at position 4 in the sterol. The final reaction is a reduction of the A7 double bond in 7-dehydro-cholesterol. An alternative pathway from lanosterol to cholesterol also exists. The enzymes involved in the transformation of lanosterol to cholesterol are all located on the endoplasmic reticulum. 

Acrylonitrile yields predominately the linear cyano aldehyde, although considerable double bond reduction takes place (equation 27).37 The reaction has received considerable attention since it is a precursor to glutamic acid via a Strecker reaction.1,2... 

Nitrodienes undergo intermolecular Diels-Alder reactions with appropriate dienophiles. The resulting nitro compounds can then be cyclized via a nitrile oxide intermediate.49 Thus, the 2-chloroacrylonitrile Diels-Alder adduct of 8-nitro-l,3-octadiene was prepared and cyclized to give (105) as a 3 1 mixture of diastereomers (Scheme 30). The Diels-Alder adduct of dimethyl acetylenedicarboxylate and 8-nitro-l,3-octadiene cyclized exclusively at the conjugated double bond, activated by the ester groups. Similarly, the quinone Diels-Alder adduct (106) cyclized at the conjugated double bond reduction of the conjugated double bond permitted cyclization on the cycloalkenyl double bond. 

B. A QUICK OUT ATTEMPTED FORMAL SYNTHESIS OF STRYCHNINE VIA A DOUBLE BOND REDUCTION TO RAWAL S INTERMEDIATE... 

The solvent attacks the mercurinium ion at the more substituted end of the double bond (where there is more <5+ charge), giving Markovnikov orientation of addition. The Hg(OAc) group appears at the less substituted end of the double bond. Reduction gives the Markovnikov product, with hydrogen at the less substituted end of the double bond. 

The intermediates in this reaction are the nine-membered VIII/99 and its isomer with a C(5),C(21) double bond. Reductions of alkaloids, VIII/98 and VTII/100 and intermediate VIII/99, with potassium borohydride in methanol, gave the same compound, VIII/101, with a medium sized ring. 

The product of double-bond reduction is a-ketobutyrate. FADH2 is the necessary enzyme cofactor. 

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