Reductions with lithium aluminium hydride

Lithium, use of, 931 Lithium aluminium hydride, reductions with, 877-881... 

Lithium aluminium hydride reduction, with inversion of the chlorosilane formed yielded the hydrosilane ([a]D + 20°). Assuming a neat inversion in the reduction step, it appeared that the formation and trapping of the silyl radical occurred with 65% retention. 

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. 

The reduction of optically active methylphenyl-n-propylphosphine sulphide with lithium aluminium hydride proceeds with 100% retention, whereas the reaction of phosphine oxides with lithium aluminium hydride leads to racemization. ... 

In the synthesis of methyl corydalate (55) Nonaka et al. (65) used the methiodide of (-t-)-tetrahydrocorysamine (65) as substrate and the Hofmann degradation method for ring opening (Scheme 16). The methine base (66) on hydroboration afforded alcohol 67, identical with a product obtained from 55 by lithium aluminium hydride reduction. 

A related strategy was used to prepare D-allosamine (134). Cycloaddition of the dipole derived from nitroacetal (129) to (S )-vinyl dioxolane (74) afforded a mixture of erythro/threo isoxazolines 130 131 (Scheme 6.72). The erythro isoxazoline was subjected to hydroxylation as described above, to give 4-hydroxyisoxazoline 132 with high diastereoselectivity. Lithium aluminium hydride reduction furnished a single diastereomer of aminodiol 133, which could be deprotected to give the hydrochloride salt of D-allosamine (134) (141). 

Any rigorous study of the oxidation of polymeric organolithium compounds should consider these products and their variation in yield with reaction conditions. To date, few of these reaction products have been considered, let alone identified and analyzed. However, the presence of the macroperoxide has been identified recently among the products of the oxidation of poly(styryl)lithium 352). Lithium aluminium hydride reduction followed by SEC analysis of the dimer fraction before and after reduction... 

Dihydromethanobenzodioxepin 155 was obtained by alkylation of benzofuranone 153 and lithium aluminium hydride reduction together with tetrahydrofurobenzofuran 154 (Scheme 42). The ring expansion to 155 probably proceeds via hemiacetal 156 <2005JOC6171>. 

Lithium aluminium hydride reduction of 235 followed by mesylation afforded 236. The latter was oxidized with osmium tetroxide and sodium metaperiodate to yield the cyclobutanone 237. Treatment of 237 with acid afforded in 48% yield the ketoacid (238), which was esterified with diazomethane to 239. The latter was converted to the ketal 240 by treatment with ethylene glycol and /7-toluenesulfonic acid. Compound 240 was reduced with lithium aluminium hydride to the alcohol 241. This alcohol had been synthesized previously by Nagata and co-workers (164) by an entirely different route. The azide 242 was prepared in 80% yield by mesylation of 241 and treatment of the product with sodium azide. Lithium aluminium hydride reduction of 242 gave the primary amine, which was converted to the urethane 243 by treatment with ethyl chloroformate. The ketal group of 243 was removed by acidic hydrolysis and the resulting ketone was nitro-sated with N204 and sodium acetate. Decomposition of the nitrosourethane with sodium ethoxide in refluxing ethanol afforded the ketone 244 in 65% yield. The latter had been also synthesized previously by Japanese chemists (165). The ketone 244 was converted to the ketal 246 and the latter to 247... 

The mixture 258 was converted to the unstable benzenesulfonyl aziridine 259 by treatment with an excess of benzenesulfonyl azide in benzene. Ace-tolysis of 259 with acetic acid and sodium acetate at room temperature for several days afforded the crystalline mixture of diastereoisomers represented by the formula 260. The aziridine rearrangement was regiospecific and 260 was the only product detected during this rearrangement. Lithium aluminium hydride reduction of 260 followed by acetylation yielded the mixture 261 in 85% yield. Selective hydrolysis of 261 afforded 262 in quantitative yield. The diastereoisomeric mixture 262 was converted into the diols 263 by hydrogenolysis. The diol mixture was oxidized with chromium trioxide... 

Lithium aluminium hydride reduction of lucidusculine (35) afforded napelline (34) in quantitative yield. Napelline was hydrogenated with platinum oxide in acetic acid to afford dihydronapelline (286). Treatment of 286 with mercuric acetate in aqueous acetic acid followed by oxidation with chromium trioxide in pyridine afforded 287 in 16.5% yield. Ketalization of 287 yielded 285 in a yield of 71%. On refluxing 285 with methanolic base, a 4 6 equilibrium mixture of 285 and 288 was obtained. These compounds... 

Since the hemiacetal 3, can now readily be prepared from cheap commercially available starting materials (vide supra, Eq. (1))7), this reaction constitutes a convenient source of 1-vinylcyclopropanols. Otherwise, the 1-ethynyl-cyclopropanols 9, also easily available from 3 or from its magnesium salt 10 (vide supra, Eq. (4) and (6) underwent either lithium aluminium hydride reduction in refluxing THF to lead exclusively to the E-1-vinylcyclopropanols 69 or reduction with dicyclopentadienyl-titanium hydride in ether at 0.°C, prepared from isobutylmagnesium halides and a catalytic amount of dicyclopentadienyl titanium dichloride (r -CjH TiCk), to yield exclusively the Z isomer 70, Eq. (22) 15,39). 

Lithium aluminium hydride reduction of 1,2-disubstituted cyclopropene-3-carboxy-lates occurs initially at the ester group, but with additional reagent good yields of cis-1,2-disubstituted-rranj-3-methanols are obtained 176). The reduction of the double bond is regioselective, leading to the more stable carbanion, and the attack of the hydride ion exclusively cis to the 3-substituent may be explained in terms of initial formation of an alkoxyaluminium complex followed by intramolecular hydride transfer 176). In the case of cyclopropene-1-carboxylates, direct reduction to the saturated alcohol occurs thus (253) is converted to the rranj-alcohol177) ... 

The n.m.r. characteristics of the isopropylidene acetals of the four possible types of ring A primary, secondary 1,3-glycol systems, exemplified by serratriol (178), lycoclavanol (179), methyl hederagenate (180), and methyl 3-epihederagenate (181), have been tabulated, and provide a useful means of differentiation.132 The reactions of the primary monotosylates of these four types provide further confirmation of stereochemistry.133 With potassium t-butoxide the cis types (178) and (181) afforded oxetans whereas the trans types (179) and (180) were converted into A-seco-aldehydes (182). Appreciable amounts of alkyl oxygen fission products were obtained on lithium aluminium hydride reduction of the monotosylates of (178), (180), and (181), presumably via participation of the 3-hydroxy-group, e.g. (183). 

The compound (70) by epoxide ring-opening with hydrogen fluoride, followed by photocatalysed addition of acetylene to the A16-bond and lithium aluminium hydride reduction, gave (71). Protection of the 1,2-diol system in (71) as the acetonide followed by oxidation, dehydration, and regeneration of the diol grouping produced... 

A series of variously substituted chloro-androstanes (17 examples), bromo-androstanes (14 examples), and amino-androstanes (29 examples) prepared from the corresponding alcohols and oximes has been described.65 It was noted during the course of this work that all ring A, B, or C oximes were reduced by lithium aluminium hydride to yield over 90% of the corresponding axial amine, except at C-3 where 65% of the equatorial amine was isolated. This is in line with the lithium aluminium hydride reduction of 5a-cholestan-3-one where the equatorial hydroxy-steroid predominates. The observation was also made that when 3/8-, 7/3-, and 16/3-tosy oxy-5a-androstanes are heated with tetra-n-butylammonium hydroxide in... 

Many achiral or chiral substituted382 and bridged 1,4-dihydropyridines383 have been prepared by a reduction of quaternary pyridium salts with sodium hydrosulphite as NADH models for enantioselective reduction of some prochiral substrates. A lithium aluminium hydride reduction of Af-acylenamines has also been observed384-386. 

Although 3,8-diamino-l ll/-dibenzo(c,/)-l,2-diazepine-5-oxide [67, R = NH2, and 67, R = N(CH3)2] were first prepared in 190651 52 by reduction of 2,2 -dinitro-4,4 -diaminodiphenylmethane with zinc dust and ammonium chloride and subsequent air oxidation in basic medium, the ring system has not received any attention until recent years. The dibenzo compounds (67, R = C1, Br, and I) were first prepared by the same method.53 The parent diazepine (68, R = H)54 and the dihalodiazepines (68, R = F, Cl, Br, and I)53 have been prepared by lithium aluminium hydride reduction of the appropriate 2,2 -dinitrodiphenylmethane. In the case of the reduction of 2,2 -dinitro-4,4 -diiododiphenylmethane, either 68 (R = H) or 68 (R = I) could be obtained depending upon the amount of reducing agent used. Attempts to prepare the system 68 by oxidation of 2,2 -diamino-diphenylmethanes led to inconclusive results.55... 

The reduction of amides to amines may be achieved with lithium aluminium hydride and with borane (Scheme 3.73). 

The di-trans isomer 206 was isolated from the products of the reaction of 190 with the bisphosphonium salt 205 in the presence of lithium ethoxide. The reaction of 207 (obtained by the oxidative coupling of 206, with dimethyl sulphate followed by reduction with sodium hydrosulphite) yielded the cyclic compound, containing the dihydropyridine nucleus, 208a. Lithium aluminium hydride reduction of 207 yielded... 

The dihydroxy-ketal (240), previously prepared from ( —)-santonin, has been used to synthesize a number of related sesquiterpenoids. Thus the diacetate of (240) was converted in six steps into (241), which was then treated with iso-propenyl acetate-sulphuric acid the derived enol-acetate was cleaved to the triol (242) by ozonolysis and lithium aluminium hydride reduction. The triol (242) was then converted into the di-iodo acetate (243) in a number of steps and thence to shyobunone (244) by dehydroiodination, reduction, and oxidation. Thermolysis of shyobunone at 160—180 °C gave preisocalamendiol (245) in about 30% yield. More recently, Iguchi et al. have shown that preisocalamendiol (245) can be cyclized to isocalamendiol (246) in aqueous acetic acid no trace of calamendiol (247) was found. A number of other interesting acid-catalysed cyclizations have been observed in this area, e.g. the formation of (248 R = OH) and (248 R = OAc) from (249) and the formation of (250) from (251). Finally, e-cadinene (252) has been obtained from (253), the lithium aluminium hydride product of preisocalamendiol (245). 

R = CHN2) followed by acid-catalysed cleavage of the resultant cyclopropyl ketone. Lithium aluminium hydride reduction of (441) gave two epimeric alcohols (443) which, on Collins oxidation, yielded the keto-aldehyde (444). Reaction of (444) with sodium triethylphosphonoacetate afforded the two isomeric keto-esters (445 R = H, R = COjEt) and (445 = CO2EL = H) which, on... 

The third synthesis, by Crombie et al., utilizes the base-catalysed condensation of the trans,trans-phenyl farnesyl sulphone (10) with trans,trans-Qthy farneso-ate to give the ester (11) as a major product via the intermediate (12). Lithium aluminium hydride reduction again yielded presqualene alcohol (1). In each case the labelled synthetic alcohol, as its pyrophosphate, was incorporated by yeast subcellular particles into squalene in ca. 68 % yield. The minor synthetic isomers were not incorporated. 

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