Compounds by hydrides

Table 3. Chiral Allenes from Propynyl Compounds by Hydride Transfer from Aluminum Hydride Reagents in THF...

It has been found that l,3-di(ethoxycarbonyl)allene reacts readily with such heterocyclic dienes as furan, pyrrole, and pyrone derivatives. The furan adduct 383, obtained in 87% yield, was hydroxylated, and after acetonation, was cleaved251 with ozone, to afford intermediate 384. An approach to the conversion of 384 into C-glycosyl compounds by hydride-promoted scission of the C-5-C-6 bond was disclosed.255... 

One of the reactions involving hydride transfer, which has synthetic importance in solution chemistry, is the Meerwein-Ponndorf-Verley reduction of carbonyl compounds by hydride transfer from alkoxide ions. Similarly, it has been found possible to reduce formaldehyde, benzaldehyde, 2,2-dimethylpropanal and 1-adamantylcarboxaldehyde with methoxide ions in the gas phase (Ingemann el al., 1982b). The reaction trajectory of the hydride transfer from the methoxide ion to formaldehyde has also been studied by ab initio calculations (Sheldon et al., 1984b). 

The reaction of azulenotropone 209 with sulfur ylide ethyl dimethyl-sulfuranylidene acetate (EDSA) )delds, instead of the expected homo-tropone, dihydro pyran 210 (82CL2027). This compound by hydride abstraction transforms to a cation (in 211a) or its mesomers that when neutralized yields tetracyclic pyran 212, the protonation of which regenerates the cation (in 211b). Pyran 212 is also obtained from dihydro compound 210 by treatment with DDQ and neutralization. 

Synthetically useful stereoselective reductions have been possible with cyclic carbonyl compounds of rigid conformation. Reduction of substituted cyclohexanone and cyclopentan-one rings by hydrides of moderate activity, e.g. NaBH (J.-L. Luche, 1978), leads to alcohols via hydride addition to the less hindered side of the carbonyl group. Hydrides with bulky substituents 3IQ especially useful for such regio- and stereoselective reductions, e.g. lithium hydrotri-t-butoxyaluminate (C.H. Kuo, 1968) and lithium or potassium tri-sec-butylhydro-borates or hydrotri-sec-isoamylborates (=L-, K-, LS- and KS-Selectrides ) (H.C. Brown, 1972 B C.A. Brown, 1973 S. Krishnamurthy, 1976). 

The Pd-catalyzed hydrogenolysis of allylic compounds by various hydrides gives alkenes. From terminal allylic compounds, either 1-alkenes or 2-alkenes are formed depending on the hydride sources [360a]. 

Uses. The largest use of lithium metal is in the production of organometaUic alkyl and aryl lithium compounds by reactions of lithium dispersions with the corresponding organohaHdes. Lithium metal is also used in organic syntheses for preparations of alkoxides and organosilanes, as weU as for reductions. Other uses for the metal include fabricated lithium battery components and manufacture of lithium alloys. It is also used for production of lithium hydride and lithium nitride. 

Hydroxypyrroles. Pyrroles with nitrogen-substituted side chains containing hydroxyl groups are best prepared by the Paal-Knorr cyclization. Pyrroles with hydroxyl groups on carbon side chains can be made by reduction of the appropriate carbonyl compound with hydrides, by Grignard synthesis, or by iasertion of ethylene oxide or formaldehyde. For example, pyrrole plus formaldehyde gives 2-hydroxymethylpyrrole [27472-36-2] (24). The hydroxymethylpyrroles do not act as normal primary alcohols because of resonance stabilization of carbonium ions formed by loss of water. 

Boron Compounds (Boron Hydrides)" in ECT 1st ed., Vol. 2, pp. 593—600, "Boron Compounds (Boron Hydride and Related Compounds)" Suppl. 1, pp. 103—130, by S. H. Bauer, Cornell University "Boron Compounds (Diborane and Higher Boron Hydrides)" Suppl. 2, pp. 109—113, byj. W. Shepherd and... 

Research Corp. "Boron Compounds (Boron Hydrides, Commercial Aspects)" in ECT3rd ed., Vol. 4, pp. 183—187, by G. B. Dunks, Union Carbide Corp. 

The chemical reduction of enamines by hydride again depends upon the prior generation of an imonium salt (111,225). Thus an equivalent of acid, such as perchloric acid, must be added to the enamine in reductions with lithium aluminum hydride. Studies of the steric course (537) of lithium aluminum hydride reductions of imonium salts indicate less stereoselectivity in comparison with the analogous carbonyl compounds, where an equatorial alcohol usually predominates in the reduction products of six-membered ring ketones. 

The reduction of carbonyl compounds by reaction with hydride reagents (H -) and the Grignard addition by reaction with organomagnesium halides (R - +MgBr) are examples of nucleophilic carbonyl addition reactions. What analogous product do you think might result from reaction of cyanide ion with a ketone ... 

Ar-Alkylations of 5//-dibenz[6,/]azcpines, e.g. 5 > 8 can be readily achieved via their nitranions, which are generated from the NH compounds by standard methodology, e.g. with sodium hydride, or sodamide, in refluxing toluene or xylene.30-J1-bt, 7° 124,1 s2 Occasionally, dioxane,187 or a mixture of tetrahydrofuran and hexamethylphosphoric triamide is used as solvent.137... 

Dibenzodiazepines are reduced to the 10,11-dihydro compounds by catalytic hydrogenation or with lithium aluminum hydride.44 ... 

H.G. Kuivii.a, Reduction of Organic Compounds by Organotin Hydrides, Synthesis 1970, 499. 

J.M. Lalancette et al., Reduction of Functional Groups with Sulfurated Borohydrides, Synthesis 1972, 526. J. Malek u. M. Cerny, Reduction of Organic Compounds by Alkoxyaluminohydrides, Synthesis 1972, 217. S.-C. Chen, Molecular Rearrangements in Lithium Aluminium Hydride Reduction, Synthesis 1974, 691. 

Isocyanates and isothiocyanates are reduced to methylamines on treatment with LiAlH4. Lithium aluminium hydride does not usually reduce azo compounds (indeed these are the products from LiAlH4 reduction of nitro compounds, 19-59), but these can be reduced to hydrazo compounds by catalytic hydrogenation or with... 

The slow step of this reaction corresponds to removal of hydride from an anion and finds several counterparts in oxidations of organic compounds by MnO. The anion may have the structure... 

The interpretation of the basis for this stereoselectivity can be made in terms of the steric, torsional, and stereoelectronic effects discussed in connection with reduction by hydrides. It has been found that crown ethers enhance stereoselectivity in the reaction of both Grignard reagents and alkyllithium compounds.119 This effect was attributed to decreased electrophilicity of the metal cations in the presence of the crown ether. The attenuated reactivity leads to greater selectivity. 

Colorless triarylmethane leuco materials 8 can be converted to carbon-ium ion (9)-colored materials, either by hydride abstraction or by chemical or photooxidation. In addition, some leuco compounds such as 11 can be converted to colored materials by treatment with an acid. The latter case is similar to the chemistry observed for fluoran (see Chapter 6) or phthalide (see Chapter 4) leuco compounds (Scheme 1). 

Dissolution of a zinc-ruthenium alloy in hydrochloric acid leaves an explosive residue of finely divided ruthenium [1], More probably this is the hydride, which may decompose on slight stimulus, the evolved hydrogen probably igniting because of the catalytic activity of the metal. Ruthenium prepared from its compounds by borohydride reduction is especially dangerous in this respect [2],... 

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