Ester hydride reduction

Hydroxyalkylthiazoles are also obtained by cyclization or from alkoxyalkyl-thiazoles by hydrolysis (36, 44, 45, 52, 55-57) and by lithium aluminium hydride reduction of the esters of thiazolecarboxylic acids (58-60) or of the thiazoleacetic adds. The Cannizzaro reaction of 4-thiazolealdehyde gives 4-(hydroxymethyl)-thiazole (53). The main reactions of hydroxyalkyl thiazoles are the synthesis of halogenated derivatives by the action of hydrobroraic acid (55, 61-63), thionyl chloride (44, 45, 63-66), phosphoryl chloride (52, 62, 67), phosphorus penta-chloride (58), tribromide (38, 68), esterification (58, 68-71), and elimination that leads to the alkenylthiazoles (49, 72). 

The introduction of tritium into molecules is most commonly achieved by reductive methods, including catalytic reduction by tritium gas, PH2], of olefins, catalytic reductive replacement of halogen (Cl, Br, or I) by H2, and metal pH] hydride reduction of carbonyl compounds, eg, ketones (qv) and some esters, to tritium-labeled alcohols (5). The use of tritium-labeled building blocks, eg, pH] methyl iodide and pH]-acetic anhydride, is an alternative route to the preparation of high specific activity, tritium-labeled compounds. The use of these techniques for the synthesis of radiolabeled receptor ligands, ie, dmgs and dmg analogues, has been described ia detail ia the Hterature (6,7). 

Mono MOM derivatives of diols can be prepared from the ortho esters by diiso-butylaluminum hydride reduction (46-98% yield). In general, the most hindered alcohol is protected. ... 

Catalytic hydrogenation of 57 affords 2-phenylacetamidopropionic acid (66) or its ester by solvolytic opening of the initially formed 5(4 )-oxazolone. Lithium aluminum hydride reduction gives the... 

Butylcyclohexanol has been prepared from />-/-butylphenol by reduction under a variety of conditions.3 4 Winstein and Holness5 prepared the pure trans alcohol from the commercial alcohol by repeated crystallization of the acid phthalate followed by saponification of the pure trans ester. Eliel and Ro 6 obtained 4-f-butylcyclohexanol containing 91% of the trans isomer by lithium aluminum hydride reduction of the ketone. Iliickel and Kurz 7 reduced />-/-butylphenol with platinum oxide in acetic acid and then separated the isomers by column chromatography. 

Analogously, for preparation of racemic carba-a-glucopyranose 49 from 52, esterification of (—)-52 furnished the ester 95, which was transformed into compound 96 by debromination with zinc dust and acetic acid. Stereoselective hydroxylation of 96 with osmium tetraoxide and hydrogen peroxide, followed by acetylation, gave compound 97. Lithium aluminum hydride reduction of 97, and acetylation of the product, gave pentaacetate 98, which was converted into 99 by hydrolysis. ... 

The products are liberated by hydrolysis of the aluminum alkoxide at the end of the reaction. Lithium aluminum hydride reduction of esters to alcohols involves an elimination step in addition to hydride transfers. 

Hydrogenation removes the benzyl group, whose function was to prevent overalkylation. Next, HBr cleaves the ether and ester groups, and either catalytic or hydride reduction completes the synthesis of 6. Separation of diastereoisomers was achieved by fractional crystallization. 

Secondary Alkyl Alcohols. Treatment of secondary alkyl alcohols with tri-fluoroacetic acid and organosilicon hydrides results only in the formation of the trifluoroacetate esters no reduction is reported to occur.1,2 Reduction of secondary alkyl alcohols does take place when very strong Lewis acids such as boron trifluoride126 129 or aluminum chloride136,146 are used. For example, treatment of a dichlo-romethane solution of 2-adamantanol and triethy lsilane (1.3 equivalents) with boron trifluoride gas at room temperature for 15 minutes gives upon workup a 98% yield of the hydrocarbon adamantane along with fluorotriethylsilane (Eq. 10).129... 

A convenient synthesis of ( )-l has been reported by Sakai et al. (105). The condensation of tryptamine with diethyl (2-formylethyl)malonate led to lactam ester 144. Deethoxycarbonylation of 144, followed by lithium aluminum hydride reduction, gave racemic octahydroindoloquinolizine (1). 

The stereoselective total synthesis of both ( )-corynantheidine (61) (170,171) (alio stereoisomer) and ( )-dihydrocorynantheine (172) (normal stereoisomer) has been elaborated by Szdntay and co-workers. The key intermediate leading to both alkaloids was the alio cyanoacetic ester derivative 315, which was obtained from the previously prepared ketone 312 (173) by the Knoevenagel condensation accompanied by complete epimerization at C-20 and by subsequent stereoselective sodium borohydride reduction. ( )-Corynantheidine was prepared by modification of the cyanoacetate side chain esterification furnished diester 316, which underwent selective lithium aluminum hydride reduction. The resulting sodium enolate of the a-formyl ester was finally methylated to racemic corynantheidine (171). 

Direct conversion of a-bromo esters into amino esters by hydride reduction of the azido ester (without isolation) produces yields in excess of 80% [7]. However, bromomalonates fail to form the azido ester under similar conditions. Instead, oxidative dimerization occurs to yield the ethene-l,l,2,2-tetracarboxylate (see Section 6.1) [10]. 

Despite the lack of diastereoselectivity and the moderate yields, the present procedure complements other syntheses of 1,3-diols such as hydride reductions of p-diketones,9 p-hydroxy ketones10 and p-keto esters,11 or the opening of 2,3-epoxy alcohols12 and 3,4-epoxy alcohols13 with Lipshutz cuprates. 

Aside from the multifaceted chemical conversions, there are sources to develop into industrially viable microbial conversions. 1,2,4-Butanetriol, for example, used as an intermediate chemical for alkyd resins and rocket fuels, is currently prepared commercially from malic acid by high-pressure hydrogenation or hydride reduction of its methyl ester. In a novel environmentally benign approach to this chemical, wood-derived D-xylose is microbially oxidized to D-xylonic acid, followed by a multistep conversion to the product effected by a biocatalyst specially engineered by inserting Pseudomonas putida plasmids into E. coli ... 

Perlmutter used an oxymercuration/demercuration of a y-hydroxy alkene as the key transformation in an enantioselective synthesis of the C(8 ) epimeric smaller fragment of lb (and many more pamamycin homologs cf. Fig. 1) [36]. Preparation of substrate 164 for the crucial cyclization event commenced with silylation and reduction of hydroxy ester 158 (85-89% ee) [37] to give aldehyde 159, which was converted to alkenal 162 by (Z)-selective olefination with ylide 160 (dr=89 l 1) and another diisobutylaluminum hydride reduction (Scheme 22). An Oppolzer aldol reaction with boron enolate 163 then provided 164 as the major product. Upon successive treatment of 164 with mercury(II) acetate and sodium chloride, organomercurial compound 165 and a second minor diastereomer (dr=6 l) were formed, which could be easily separated. Reductive demercuration, hydrolytic cleavage of the chiral auxiliary, methyl ester formation, and desilylation eventually led to 166, the C(8 ) epimer of the... 

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