Diisobutylaluminium hydride reduction with

Yamauchi et al. completed an ex-chiral pool synthesis of a samin-type lignan, Scheme (38) [102]. The diprotected tetraol 230 was obtained from Z-glutammic acid by a 15 step procedure in 7-8% overall yield [103]. The diprotected tetraol 230 was treated with boron trifluoride diethyl etherate in dichloromethane to give the tetrahydrofuran 231 in 84%-87% yield. After deprotection with tetrabutylammonium fluoride, the resulting diol was oxidized by dihydridotetrakis(triphenylphospine)ruthenium(II) to provide two lactones 232 and 233 in a ratio of 2 1. Lactone 232 was transformed in samin-type lignan 234 by diisobutylaluminium hydride reduction in 70% yield. 

Enantiomerically pure /J-keto sulfoxides are prepared easily via condensation of a-lithiosulfinyl carbanions with esters. Reduction of the carbonyl group in such /J-keto sulfoxides leads to diastereomeric /J-hydroxysulfoxides. The major recent advance in this area has been the discovery that non-chelating hydride donors (e.g., diisobutylaluminium hydride, DIBAL) tend to form one /J-hydroxysulfoxide while chelating hydride donors [e.g., lithium aluminium hydride (LAH), or DIBAL in the presence of divalent zinc ions] tend to produce the diastereomeric /J-hydroxysulfoxide. The level of diastereoselectivity is often very high. For example, enantiomerically pure /J-ketosulfoxide 32 is reduced by LAH in diethyl ether to give mainly the (RR)-diastereomer whereas DIBAL produces exclusively the (.S R)-diastereomer (equation 30)53-69. A second example is shown in... 

The silane, prepared by reduction of tris(2-propylthio)silylenium perchlorate with diisobutylaluminium hydride at —78°C, is subsequently isolated by high-vacuum distillation from the mixture. Heating must be very mild to prevent explosion. 

Enantiospecific syntheses of amino derivatives of benzo[ ]quinolizidine and indolo[2,3- ]quinolizidine compounds have also been achieved via A-acyliminium ion cyclization reactions, as an alternative to the more traditional Bischler-Napieralski chemistry (see Section 12.01.9.2.2). One interesting example involves the use of L-pyroglutamic acid as a chiral starting material to construct intermediates 240 via reaction with arylethylamine derivatives. Diisobutylaluminium hydride (DIBAL-H) reduction of the amide function in 240 and subsequent cyclization and further reduction afforded piperidine derivatives 241, which stereoselectively cyclized to benzo[ ]quinolizidine 242 upon treatment with boron trifluoride (Scheme 47) <1999JOC9729>. 

Treatment of the amide 210 with diisobutylaluminium hydride (DIBAL-H) produces not only the expected reduction product 211 but also gives a mixture of the pyrrolonaphthyridine 212 and the indoloquinoline 213. Treatment of 212 with 50% acetic acid results in rearrangement to 213 (Equation 54) <1996JOC7882>. 

Esters 154 (R = C02Me) undergo reduction by treatment with diisobutylaluminium hydride (DIBAL-H) to form alcohols 154 in 17% yield (R = CH2OH) <2006BML1207>. 

In order to establish the correct absolute stereochemistry in cyclopentanoid 123 (Scheme 10.11), a chirality transfer strategy was employed with aldehyde 117, obtained from (S)-(-)-limonene (Scheme 10.11). A modified procedure for the conversion of (S)-(-)-limonene to cyclopentene 117 (58 % from limonene) was used [58], and aldehyde 117 was reduced with diisobutylaluminium hydride (DIBAL) (quant.) and alkylated to provide tributylstannane ether 118. This compound underwent a Still-Wittig rearrangement upon treatment with n-butyl lithium (n-BuLi) to yield 119 (75 %, two steps) [59]. The extent to which the chirality transfer was successful was deemed quantitative on the basis of conversion of alcohol 119 to its (+)-(9-methyI mande I ic acid ester and subsequent analysis of optical purity. The ozonolysis (70 %) of 119, protection of the free alcohol as the silyl ether (85 %), and reduction of the ketone with DIBAL (quant.) gave alcohol 120. Elimination of the alcohol in 120 with phosphorus oxychloride-pyridine... 

In a similar procedure, through diisobutylaluminium hydride (DIBALH)-reduction of nitrile into imine and condensation with A-benzylhydroxylamine, C-(l-fluorovinyl) nitrones were synthesized (Scheme 2.30, Table 2.4) (228). 

Purine nucleosides of type 1.4 (1177) were prepared by the reductive cleavage at the anomeric position of the ribofuranosyl moiety of 1176 with diisobutylaluminium hydride (DIBALH). The reductive ring opening was explained by the initial formation of a Lewis complex (93TL4835). 

Reduction of 166 with NaBH4/CeCl3 in aqueous MeOH afforded the protected, chiral derivative 169 of Conduritol-D in 73 % yield. Conduritol-D (170) was formed nearly quantitatively upon acid hydrolysis of 169. Treatment with Ac20/pyridine gave the crystalline tetracetate 171. Reduction of 165 with diisobutylaluminium hydride (DIBAL) in toluene (-80 °C, 6 h) gave 172, another chiral derivative of Conduritol-D, in 97 % yield. Alternatively, 167 was reduced with LiAlH4 (THF, -90 °C, 6 h) into 173 (95 %). Deprotection of 167 with tetrabutylammonium fluoride... 

The tetrahydro-l,4-oxazin-2-ones are lactones and have been reduced to the corresponding hemiacetals (tetrahy-dro-l,4-oxazin-2-ols) using diisobutylaluminium hydride <1998T10419> and lithium triisobutylborohydride <2004TL8917>. Rather remarkably, treatment of the tricyclic tetrahydro-l,4-oxazin-2-one 210 with LAH and boron trifluoride results in complete reduction of both carbonyl groups to afford the tetrahydro-l,4-oxazine 211 (Equation 15) <1978CB1164>. 

The ylide 140 <2000JOC8068> is stable to attempted reduction using sodium borohydride, diisobutylaluminium hydride (DIBAL-H), or lithium aluminium hydride <2000JOC6388>, but eliminates propene on heating to form the annulated parent 141. Oxidation of the latter with lead(iv) oxide and potassium carbonate forms a radical, 142, which is stable to chromatography and can be stored in air for several days. 

Aldehydes are prepared by the hydroboration-oxidation of alkynes (see Section 5.3.1) or selective oxidation of primary alcohols (see Section 5.7.9), and partial reduction of acid chlorides (see Section 5.7.21) and esters (see Section 5.7.22) or nitriles (see Section 5.7.23) with lithium tri-terr-butox-yaluminium hydride [LiAlH(0- Bu)3] and diisobutylaluminium hydride (DIBAH), respectively. 

Chlorophenyl)glutarate monoethyl ester 87 was reduced to hydroxy acid and subsequently cyclized to afford lactone 88. This was further submitted to reduction with diisobutylaluminium hydride to provide lactol followed by Homer-Emmons reaction, which resulted in the formation of hydroxy ester product 89 in good yield. The alcohol was protected as silyl ether and the double bond in 89 was reduced with magnesium powder in methanol to provide methyl ester 90. The hydrolysis to the acid and condensation of the acid chloride with Evans s chiral auxiliary provided product 91, which was further converted to titanium enolate on reaction with TiCI. This was submitted to enolate-imine condensation in the presence of amine to afford 92. The silylation of the 92 with N, O-bis(trimethylsilyl) acetamide followed by treatment with tetrabutylammonium fluoride resulted in cyclization to form the azetidin-2-one ring and subsequently hydrolysis provided 93. This product was converted to bromide analog, which on treatment with LDA underwent intramolecular cyclization to afford the cholesterol absorption inhibitor spiro-(3-lactam (+)-SCH 54016 94. 

The ester 168 on reduction with diisobutylaluminium hydride (DIBAL-H) followed by the treatment with amino alcohol, (C6Hs)2C(OH)CH2NH2, followed by reduction led to the formation of intermediate 169, which was... 

Thus two successive oxidations of 429 (Scheme 59) involving the Jones reagent and dichlorodicyano-p-benzoquinone respectively led to the enone 430. A similar reductive cleavage as above of the derived dimethyl acetal 431 with diisobutylaluminium hydride occurred from the less hindered a-side to furnish the P-methoxyether 432 as the major isomer. Selective O-debenzylation of432, achieved with iodotrimethylsilane led to ( )-coccinine (413). 

Chiral addition of allyl metals to imines is one of the useful approaches toward the synthesis of homoallylic amines. These amines can be readily converted to a variety of biologically important molecules such as a-, / -, and y-amino acids. Itsuno and co-workers utilized the allylborane 174 derived from diisopropyl tartrate and cr-pinene for the enantioselective allylboration of imines. The corresponding iV-aluminoimines 173 are readily available from the nitriles via partial reduction using diisobutylaluminium hydride (DIBAL-H) <1999JOM103>. Recently, iV-benzyl-imines 176 have also been utilized for the asymmetric allylboration with allylpinacol boronate 177 in the presence of chiral phosphines as the chiral auxiliaries to obtain homoallylic A -benzylamines 178 in high yield and selectivity (Scheme 29) <2006JA7687>. 

Sulfone 47 was prepared in nine steps from known iodide 69 by the sequence shown in Scheme 17.15. After initial conversion of 69 into aldehyde 70 by cyanide displacement and reduction with diisobutylaluminium hydride (DIBAL), a Corey-Fuchs alkynylation25 yielded alkyne 51, the key substrate needed for the proposed carboalumination-epoxide ring-opening step. Carboalumination26 was achieved by treating... 

Lactam 86, when treated with diisobutylaluminium hydride (DIBAL-H), led to a 6 2 1 mixture of 89b, 90b, and 91b (95% combined yields) (Scheme 20) <1996T3563>. In the case of reaction of 83 with l-(2-hydroxy-l-phenylethyl)-5,6-dihydropyridin-2(l//)-one, an equimolecular mixture of cis- and trans-lactams of type 85 (R = CH(Ph)CH2OH, R = R2 = H) was obtained in 88% yield. Reduction of the trans-lactam with Red-Al gave the diazocine 89 (R = CH(Ph)CH2OH) and an analogue of 91 with an oxazolidine ring annelated to the piperidine moiety <1995TL1693>. 

Epoxidation of oxonine 93 with dimethyldioxirane, followed by reduction with diisobutylaluminium hydride (DIBAL-H), resulted in a separable mixture of alcohols 95 and 96, and the side product 94 (Scheme 16). Each of the isomers was submitted to Swern oxidation and sequential stereoselective reduction with L-selectride to achieve desired stereochemistry of the products 97 and 98. Formation of the side product 94 was explained by Lewis acidity of DIBAL-H and confirmed by treatment of oxirane derived from 93 with another Lewis acid, AlMe3, to produce oxocine aldehyde 99 in 35% isolated yield <1997CL665>. Similar oxidative synthetic sequence was utilized for the synthesis of functionalized oxonines as precursors of (-l-)-obtusenyne <1999JOG2616>. 

Reduction of enone 717 with diisobutylaluminium hydride (DIBAL) or thioindoxyls 719 with NaBH4 followed by spontaneous dehydration gives the thiophene 718 <2002TL8485> or benzothiophenes 720 <2002SL325, 2003T4767>, respectively. 

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