Reduction regiospecific

Reductive animation, 930-932 amino acid synthesis and, 1026 biological example of, 932 mechanism of, 931 Refining (petroleum). 99-100 Regiospecific, 191... 

Formal isomerization of the double bond of testosterone to the 1-position and methylation at the 2-position provides yet another anabolic/androgenic agent. Mannich condensation of the fully saturated androstane derivative 93 with formaldehyde and di-methylamine gives aminoketone 94. A/B-trans steroids normally enolize preferentially toward the 2-position, explaining the regiospecificity of this reaction. Catalytic reduction at elevated temperature affords the 2a-methyl isomer 95. It is not at all unlikely that the reaction proceeds via the 2-methylene intermediate. The observed stereochemistry is no doubt attributable to the fact that the product represents the more stable equatorial isomer. The initial product would be expected to be the p-isomer but this would experience a severe 1,3-diaxial non-bonded interaction and epimerize via the enol. Bromination of the ketone proceeds largely at the tertiary carbon adjacent to the carbonyl (96). Dehydrohalogenation... 

Reduction of the heterocyclic ring and incorporation of a nitro function affords a compound with antischistosomal activity, oxamniquine (60). Its synthesis begins with chlorination of 2,6-dimethyl-quinoline, which proceeds regiospecifically on the methyl group adjacent to the ring nitrogen (56). 

The regiospecificity of the exclusive O-acylation [8] and O-phosphorylation [9] of P-dicarbonyl compounds (Chapter 3) also illustrates the effect of phase-transfer catalysts on the stereochemical course of reactions. Similarly, directed reduction of P-hydroxy ketones using tetramethylammonium trisacetoxyborohydride leads to the preferential formation of the anti dihydroxy system in high yield with a stereoselectivity >95% [10] (Section 11.4). 

More frequent than the deoxygenation of epoxides to alkenes is reduction of epoxides to alcohols. Its regiospecificity and stereospecificity depend on the reducing agents. 

Sauers and coworkers have applied the Paterno-Biichi reaction to engeneral formula 427 (Scheme XXXIV) Reductive cleavage of these products with lithium aluminium hydride is also regioselective and leads, following oxidation, to ketones... 

In work which remains unpublished, Wenkert has succeeded in cleverly transforming 2-methylcyclopentanone into isocomene The key elements of his strategy (Scheme LXXXIII) are the acid-catalyzed ring expansion of methoxycyclopropane 747 to 748 and the regiospecific homologation of the cyclobutanone to 749. Unfortunately, the Wolff-Kishner reduction of this penultimate intermediate affords both 731 and its epimer. 

Section 1.1.1.3.1.1.2.1.). Similarly, the reductive ring opening of cyclopropyl ketones, e.g., 8, with lithium in ammonia affords specific enolates20,21. These enolates can, of course, be used for selective alkylation. Furthermore, enol acetates, e.g., 10, are regiospecifically obtained by nucleophilic ring opening of cyclopropyl ketones21. 

Oxymercuration-reduction of alkenes preparation of alcohols Addition of water to alkenes by oxymercuration-reduction produces alcohols via Markovnikov addition. This addition is similar to the acid-catalysed addition of water. Oxymercuration is regiospecific and auft -stereospecific. In the addition reaction, Hg(OAc) bonds to the less substituted carbon, and the OH to the more substituted carbon of the double bond. For example, propene reacts with mercuric acetate in the presence of an aqueous THF to give a hydroxy-mercurial compound, followed by reduction with sodium borohydride (NaBH4) to yield 2-propanol. 

This reduction was useful in a synthesis of a thromboxane B intermediate (9) from 6, prepared in a few steps from a readily available carbohydrate levoglucosan. Hydride reduction of 6 to 7 is regiospecific because of the a-allyl group. RuOz-NalOA oxidation (2, 358-359) gives the tricyclic lactone 8, which is cleaved by Amberlyst 15 in methanol to 9 and 10. The a-isomer 9 has been converted to thromboxane B2 (II) in two laboratories.3... 

Dolfing, J. (1995). Letter to the editor Regiospecificity of chlorophenol reductive dechlorination by Vitamin B12s. Applied and Environmental Microbiology, 6l, 2450-1. 

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