Reduction LiAlH

Enolates also serve as suitable reaction partners in a directed aldol condensation (Eq. 52) 88) Dehydration of the aldol 51 to give enone (POCl3, HMPA then C5H5N) followed by reduction [LiAlH(nC4H9) (iC4H9)2] produces a vinylogue of a cyclopropylcarbinol 53. Aqueous fluoroboric acid smoothly rearranges 53 to the... 

Hapepunine (72), occurring in Fvitillavia aamtsahataensis, is the first natural 166-hydroxy-22,26-epiminocholestane derivative encountered (Mitsuhashi et al., Tetrahedron Letters, 1978, 2099). Anrakorinine, from the same source, affords a tosylate which on reduction (LiAlH ) yields hapepunine (72). In its pmr-spectrum it lacks a methyl singlet at 6 0.96 ppm (present in hapepunine), but has an AB quartet (2H) at 3.62 and 3.88 ppm. Consequently it is formulated as 18-hydroxyhapepunine (73) idem, Phytochem., 1981, M, 157). Several indolizidine bases, also related to Solarium Alkaloids, have been encountered in the Fritil-laria group. Camtschatcanidine, for example, from F. aamtsohatoensis, is (74), on the basis of spectral comparison with solanidine on reduction (LiAlHi ) of its 0-tosyl-derivative solanidine (75) is formed (Mitsuhashi et al.. 

Interestingly, the reduction (LiAlH/j), or the Grignard reaction (CH3MgI), of the ketal tosylate 376 gave ketal 378 (R=H or CH3) (109). The two oxygens of the ketal function in 376 have each an electron pair oriented antiperi-planar to ease the fragmentation process to give the dioxolenium ion intermediate 377. 

Reduction LiAlH THF solution, room temperature 4.5 h, 0.1 M HCl Hydroxyl groups 30... 

The methyl glycosides (107) and (108) of D-quinovosamine and D-fucosamine have been synthesised in several steps from 2-acetamido-2-deoxy-D-glucose and -D-galactose, respectively. The required 6-deoxygenations were effected by reduction (LiAlH ) of 6-tosylates. The known unsaturated nitro-sugar (109) has been reduced (NaBH then Ha - Pt - HCl) to the 3-amino-3,4,6-trideoxy-a-... 

Lithium aluminium hydride, LiAlH, is a very active reducing agent, and is used particularly for the ready reduction of carboxylic acids (or their esters) to primary alcohols R-COOH -> R CH,OH. 

Lithium aluminium hydride LiAlH is a useful and conveuient reagent for the selective reduction of the carbonyl group and of various other polar functional groups. It is obtained by treatment of finely powdered lithium hydride with an ethereal solution of anhydrous aluminium chloride ... 

If it is necessary to reduce one group in a given molecule without affecting any other unprotected reducible group, the following reactivity orders for ease of reduction toward catalytic hydrogenation, LiAlH, and diborane may serve as a guideline. 

Another possibility for asymmetric reduction is the use of chiral complex hydrides derived from LiAlH. and chiral alcohols, e.g. N-methylephedrine (I. Jacquet, 1974), or 1,4-bis(dimethylamino)butanediol (D. Seebach, 1974). But stereoselectivities are mostly below 50%. At the present time attempts to form chiral alcohols from ketones are less successful than the asymmetric reduction of C = C double bonds via hydroboration or hydrogenation with Wilkinson type catalysts (G. Zweifel, 1963 H.B. Kagan, 1978 see p. 102f.). 

The hydrogenolyaia of cyclopropane rings (C—C bond cleavage) has been described on p, 105. In syntheses of complex molecules reductive cleavage of alcohols, epoxides, and enol ethers of 5-keto esters are the most important examples, and some selectivity rules will be given. Primary alcohols are converted into tosylates much faster than secondary alcohols. The tosylate group is substituted by hydrogen upon treatment with LiAlH (W. Zorbach, 1961). Epoxides are also easily opened by LiAlH. The hydride ion attacks the less hindered carbon atom of the epoxide (H.B. Henhest, 1956). The reduction of sterically hindered enol ethers of 9-keto esters with lithium in ammonia leads to the a,/S-unsaturated ester and subsequently to the saturated ester in reasonable yields (R.M. Coates, 1970). Tributyltin hydride reduces halides to hydrocarbons stereoselectively in a free-radical chain reaction (L.W. Menapace, 1964) and reacts only slowly with C 0 and C—C double bonds (W.T. Brady, 1970 H.G. Kuivila, 1968). 

The reactions of NaAlH are the same as those of LiAlH. However, it is much less soluble THF is the only good solvent. Heterogeneous reductions in good yield with NaAlH in hydrocarbon media have been reported (49). 

Commercially, pure ozonides generally are not isolated or handled because of the explosive nature of lower molecular weight species. Ozonides can be hydrolyzed or reduced (eg, by Zn/CH COOH) to aldehydes and/or ketones. Hydrolysis of the cycHc bisperoxide (8) gives similar products. Catalytic (Pt/excess H2) or hydride (eg, LiAlH reduction of (7) provides alcohols. Oxidation (O2, H2O2, peracids) leads to ketones and/or carboxyUc acids. Ozonides also can be catalyticaHy converted to amines by NH and H2. Reaction with an alcohol and anhydrous HCl gives carboxyUc esters. 

Table 5. Yields of Organosilanes via Reduction with LiAlH and LiH ...

Constmction of multilayers requires that the monolayer surface be modified to a hydroxylated one. Such surfaces can be prepared by a chemical reaction and the conversion of a nonpolar terminal group to a hydroxyl group. Examples of such reactions are the LiAlH reduction of a surface ester group (165), the hydroboration—oxidation of a terminal vinyl group (127,163), and the conversion of a surface bromide using silver chemistry (200). Once a subsequent monolayer is adsorbed on the "activated" monolayer, multilayer films may be built by repetition of this process (Fig. 8). 

The reduction of (aLkylarnino)haloboranes using hydride reagents can provide a convenient route to (aLkylamino)boranes for example, LiAlH has been utilized to prepare bis (dimethyl amino)borane [23884-11-9] from chi orobis (dimethyl amino)borane [6562-41-0] (68). When this same strategy is appHed to (bis(trimethylsi1y1)amino)ch1oro((trimethylsi1y1)amino)borane [10078-93-0] the expected compound is obtained along with the formation of two... 

Reduction with Metals and Metal Hydrides. Practically any ester can be reduced by Na—C2H OH, Li or Na—NH, LiAlH, LiBH, or NaBH to give alcohols in excellent yield (35,36). Carbon-carbon double bonds are usually preserved using these reducing reagents. 

LiAlH —(C2H )2NH. The use of BH or LiAlH —BE 0(C2H )2 as a reducing reagent converts esters to ethers. Thus, reduction of esters can be manipulated by the judicious selection of metal-containing reducing reagents. 

In principle, complex hydrides (NaBHj, LiAlH ) ought to react similarly with 4-pyrones and lead after treatment with Bronsted or Lewis acids to 4-unsubstituted pyrylium salts. This reaction has not been reported the reduction of 2-pyrones with LiAlH4 results in ring opening. " ... 

Conversion of Amides into Amines Reduction Like other carboxylic acid derivatives, amides can be reduced by LiAlH.4. The product of the reduction, however, is an amine rather than an alcohol. The net effect of an amide reduction reaction is thus the conversion of the amide carbonyl group into a methylene group (C=0 —> CTbV This kind of reaction is specific for amides and does not occur with other carboxylic acid derivatives. 

Harrison, J. Fuller, J.C. Goralski, C.T. Singaram, B. Tetrahedron Lett., 1994, 35, 5201. Boireau, G. Deberly, A. Toneva, R. Synlett, 1993, 585. In this study, reduction with LiAlH(Or-Bu)3 was shown to give primarily the trans-alcohol. 

Norbomenone 26 undergoes reduction by sodium borohydride under kinetic conditions to produce 5% exo- (i.e., endo attack) and 95% endo- (i.e., exo attack) 2-norbomeol. This leads to the partial rate constants of 11.4 for exo and 0.6 for endo attack (relative rate with respect to the rate of LiAlH reduction of cyclopen-tanone (1.00)) [80]. In the saturated 2-norbomanone 25, the values are 4.55 for exo and 0.74 for endo attack. Thus, the introduction of the double bond enhances the... 

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