Metal hydride reducing

Metal hydrides reduce preferably polar double bonds, whereas catalytic hydrogenation is somewhat selective for non-polar double bonds. Selective protection of amino groups in amino acids. 

For most laboratory scale reductions of aldehydes and ketones catalytic hydro genation has been replaced by methods based on metal hydride reducing agents The two most common reagents are sodium borohydride and lithium aluminum hydride... 

Sulphoxides are reduced by the more powerful metal hydride reducing agents14, but the less reactive reagents such as sodium borohydride are ineffective. Recently, Yoon25 has... 

The other way of reducing nitriles to aldehydes involves using a metal hydride reducing agent to add 1 mol of hydrogen and hydrolysis, in situ, of the resulting imine (which is undoubtedly coordinated to the metal). This has been carried out with LiAlH4, LiAlH(OEt)3, LiAlH(NR2)3, and DIBAL-H. The metal hydride method is useful for aliphatic and aromatic nitriles. 

One study showed that the Cram s mle product predominates with metal hydride reducing agents, but the other product with Bouveault-Blanc and dissolving metal reductions Yamamoto, Y. Matsuoka, K. Nemoto, H. J. Am. Chem. Soc., 1988, 110, 4475. 

See other gas evolution incidents See other metal hydrides, reducants... 

Alkali metal hydrides reduce boron trichloride to diborane at ordinary temperatures ... 

CO formation on copper electrodes appears to be accompanied by hydride formation as well [103]. In Sch. 3, the surface bound CO is reduced by a hydride transfer reaction to form a formyl species as shown in step 2. There are precedents in organometallic chemistry for late transition metal hydrides reducing bound CO [105-109]. Protonation of the adsorbed formyl in step 3 results in the formation of a hydroxy carbene species [110, 111]. This hydroxycarbene species could be considered to be an adsorbed and rearranged form of formaldehyde, and the reduction of formaldehyde at a copper electrode has been reported to form hydrocarbons [102]. However, reduction of... 

For discussions of selectivity with metal hydride reducing agents, sec Brown Krishnamurthy Tetrahedron, 1979, 35. 567-607 Walker Chem. Soc. Rev. 1976,5, 23-50 Brown Boranes in Organic Chemistry, Cornell University Press Ithaca. NY, 1972, pp. 209-251, Rerick, in Augustine, Ref. 486. For books, sec, in Ref. 10, the works by Seydcn-Pcnnc, Strouf ct al. and Hajds. 

Catalytic reduction of steroid epoxides received considerable attention before the development of complex metal hydride reducing agents. Hydrogenation of 3 ,4a-epoxy steroids over platinum in acetic acid (Eq. 360), for example, gives rise to a mixture of 3 -hydroxy and 3 -acetoxy steroids.Reductive cleavage thus occur in the same direction as with lithium aluminium hydride in this particular instance —t.r. it gives an axis alcohol. 

Now, if a metal-hydride reducing agent, such as LiAlH4, is present, the carbonyl group of 10 is reduced and 11 is formed ... 

A variety of metal hydride reducing agents can also function in this reaction. Sodium botohydride, for example, has demonstrated good regioselectivity, with preferential delivery of the hydride to the less substituted allyl terminus (equation 93).285-287 Allyl sulfones are substituted by hydride under Pd catalysis and treatment with NaBH4 (equation 94).288-289 Sodium cyanoborohydride functions in like manner.290... 

One of the uses of these ester-acyl chlorides is for the synthesis of co-hydroxy esters which involves the selective reduction of the acyl chloride grouping with sodium borohydride161 the alkoxycarbonyl group is unaffected by this metal hydride reducing agent (cf. Section 5.4.1, p. 519). 

Other methods of reduction include the use of metal-acid systems, catalytic hydrogenation over Raney nickel or palladium-on-charcoal, and modified metal hydride reducing agents such as Red-Al .209... 

Metal hydrides reduce 1-a-anomeric halosugars into l- 3-deoxy sugars with inversion of configuration by a SN2 mechanism. On the contrary, the use of Bu3SnD under photochemical conditions yields deoxy sugars with retention of configuration with a stereoselectivity of 90% according to Scheme 4 [17a]. 

See other GAS EVOLUTION INCIDENTS, METAL HYDRIDES, REDUCANTS... 

Interaction of anhydrous hydrazine and titanium isopropoxide is explosive at 130°C in absence of solvent. Evaporation of solvent ether from the reaction product of tetra-kis(dimethylamino)titanium and anhydrous hydrazine caused an explosion, attributed to formation and ignition of dimethylamine. /V-Metal derivatives may also have been formed. See Other NON-METAL HYDRIDES, REDUCANTS... 

Sodium tetrahydroborate, 0147 Sodium tetrahydrogallate, 4402 Tricyclopentadienyluranium tetrahydroaluminate, 3681 Uranium(III) tetrahydroborate, 0178 Uranium(IV) tetrahydroborate etherates, 0183 Zirconium(IV) tetrahydroborate, 0184 See also METAL HYDRIDES See other NON-METAL HYDRIDES, REDUCANTS... 

This method is an inexpensive substitute for LAH reductions of esters in industrial production, and was the only alternative prior to the development of the metal hydride reducing agents. This dissolving metal reduction is also related to the Birch Reduction. 

Unsymmetrically substituted benzylidene acetals can be cleaved regioselectively in some cases using Lewis acidic metal hydride reducing agents.317 The cleavage results in the formation of a benzyl ether (more hindered position) and an alco-... 

Because so many of the recent developments in reduction methodology have involved metal hydride reducing agents, this chapter inevitably has an old-fashioned flavor. Most of the methods described below originated many years ago, and many of them do not figure prominently in the current literature. However, this is not to say that they have no value. In many cases they are economical and suitable for large scale use, and it is quite likely that the best way to make substantial amounts of a simple aldehyde (especially an aromatic one) will be found in this chapter. Moreover, there are some cases where recent improvements, which may not be widely appreciated, have given a classical method a new lease of life. The reader is directed particularly to the amine-modified Rosenmund described in Section 1.12.3. 

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