Improved procedure for the asymmetric reduction of prochiral ketones by B-3-pinanyl-9-borabicyclo[3.3.1]nonane

Brown, Herbert C.; Pai, Ganesh G.

doi:10.1021/jo00347a058

Cited by 57 publications

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“…Following Brown, 31 9-BBN dimer (11.2 g, 92 mmol) and (Ϫ)-α-pinene (14.6 cm 3 , 91 mmol) were stirred together and heated at 65 ЊC under argon for 5 h. The mixture was cooled to room temperature and 4-trimethylsilylbut-3-yn-2-one 70 (6.4 g, 46 mmol) was added. The orange mixture was stirred at room temperature for 18 h, then cooled to 0 ЊC.…”

Section: (2s )-4-trimethylsilylbut-3-yn-2-ol 27mentioning

confidence: 99%

Accurate determinations of the extent to which the SE2? reactions of allyl-, allenyl- and propargylsilanes are stereospecifically anti

et al. 2004

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The allylsilanes, (R)-E- and (R)-Z-4-trimethylsilylpent-2-ene 16, were prepared in essentially an enantiomerically and geometrically pure state (er >99.95 : 0.05, E : Z and Z : E >99.95 : 0.05) by, successively, conjugate addition of lithium dimethylcuprate to N-[(E)-3'-trimethylsilylpropenoyl]-(7S)-10,10-dimethyl-4-aza-5-thiatricyclo[5.2.1.0(3,7)]decane 5,5-dioxide 13, to give N-[(E)-(3'R)-3'-trimethylsilylbutanoyl]-(7S)-10,10-dimethyl-4-aza-5-thiatricyclo[5.2.1.0(3,7)]decane 5,5-dioxide, removal of the chiral auxiliary with bromomagnesium benzyloxide, aldol reaction with acetaldehyde, and decarboxylative elimination, to give either the Z- or E-isomer. Both the E- and Z-allylsilanes 16 reacted with the adamantyl cation to give mixtures of E- and Z-4-adamantylpent-2-enes 17. The E-allylsilane gave the E- and Z-products in a ratio of 40 : 60, and the Z-allylsilane gave the E- and Z-products in a ratio of 99.8:0.02. The enantiomer ratio was >99:1 for the reaction of the E-allylsilane giving the Z-product, 90:10 for the E-allylsilane giving the E-product, and 95 : 5 for the Z-allylsilane giving the E-product, showing that the reactions were stereospecific to a high degree, but not always quite completely so. The allenylsilane, 2-trimethylsilylpenta-2,3-diene 29, was prepared enantiomerically highly enriched (er 99:1) by copper-catalysed reaction of methylmagnesium chloride with (S)-4-trimethylsilylbut-3-yn-2-yl camphor-10-sulfonate 28. The allenylsilane 29 reacted with the adamantyl cation to give (S)-4-adamantylpent-2-yne (S)-30 with the same level of enantiomeric purity, showing that the reaction was, as accurately as can be measured, completely stereospecific. The allenylsilane 29 also reacted with isobutanal in the presence of titanium tetrachloride to give 2,4-dimethylhept-5-yn-3-ol as a mixture of diastereoisomers, syn 31 and anti 32, in a ratio of 95:5, with the major diastereoisomer present as a mixture of enantiomers (4R,5R):(4S,5S) in a ratio of 99:1, showing that the reaction was, as accurately as can be measured, completely stereospecific in the anti sense. The corresponding propargylsilane, 4-trimethylsilylpent-2-yne 37, reacted with the adamantyl cation to give dienes assigned the structures 2,3-diadamantyl-1,3-pentadiene 42 and 2,4-diadamantyl-1,3-pentadiene 43, and reacted with isobutanal in the presence of titanium tetrachloride to give 2-(1-hydroxy-2-methylpropyl)-3-trimethylsilylpenta-1,3-dienes 45 and 2,4-dimethyl-5-trimethylsilylhept-5-en-3-one 46. The enantiomerically enriched propargylsilane (R)-1,3-bis(trimethylsilyl)but-1-yne (er >99.7:0.3) was prepared from the sultam 13, by removal of the chiral auxiliary with lithium ethoxide, reduction of the ethyl ester to give (R)-3-trimethylsilylbutanal 60, enol triflate formation, beta-elimination and C-silylation. The propargylsilane reacted with 2,4-dinitrobenzaldehyde in the presence of titanium tetrachloride to give the allenes, 1-(2,4-dinitrophenyl)-2-trimethylsilylpenta-2,3-dienols 63-66, as two diastereoisomers in a ratio of 2 : 1, each of whi...

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Section: (2s )-4-trimethylsilylbut-3-yn-2-ol 27mentioning

confidence: 99%

Accurate determinations of the extent to which the SE2? reactions of allyl-, allenyl- and propargylsilanes are stereospecifically anti

et al. 2004

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“…Completion of the synthesis of key intermediate 2 was uneventful (Scheme ). Lithium borohydride reduction of 53 provided a mixture of allylic alcohols 54a/54b which only differ in that 54a suffered acetate cleavage at C3 during borohydride treatment. This mixture was selectively reoxidized to a corresponding mixture of aldehydes 55/2 with MnO 2 .…”

Section: Conversion Of Hecogenin Acetate 1 To Aldehydementioning

confidence: 99%

Synthesis of the North 1 Unit of the Cephalostatin Family from Hecogenin Acetate¹

et al. 1999

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Hecogenin acetate (1) was converted to North 1 azidoketone 5 involving several key transformations: (1) conversion of cyclic sulfate 33b to allylic alcohol 40 via Reich iodoso olefination; (2) E-ring annulation via intermolecular oxygen alkylation of highly functionalized secondary alcohol 40 using rhodium-catalyzed decomposition of an α-diazophosphonoacetate to provide α-alkoxyphosphonoacetate 52, with subsequent intramolecular Wadsworth−Emmons reaction to provide alkoxydihydrofuran 53; and (3) establishment of the C20 stereochemistry by chromium(II) reduction of tertiary bromide 86 to a 9:1 mixture of diastereomeric spiroketals 90α/90β, separated as silyl ethers 91α/91β. Conversion of 91α to α-azidoketone 5 was uneventful.

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“…1,2,3,4-Tetrahydroisoquinoline-3carboxylic acid (9) was reacted with 2-fluoronitrobenzene (10) and the resulting carboxylic acid was esterified directly by treatment with dimethyl sulfate under basic conditions giving the ester 11. Reduction of ester 11 was achieved by treatment with lithium borohydride in the presence of trimethoxyborane yielding the alcohol 12 [5]. When the alcohol 12 was treated with 4-toluenesulfonyl chloride in pyridine, unexpectedly, the chloride 13 was obtained.…”

mentioning

confidence: 99%

Possible neighbouring group participation of a nitro-group in the conversion of 3-hydroxymethyl-2-(2-nitrophenyl)-1,2,3,4-tetrahydroisoquinoline into its 3-chloromethyl derivative

Donaghy

Stanforth

2005

Journal of Heterocyclic Chemistry

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The alcohol 12 reacted with 4-toluenesulfonyl chloride in boiling dichloromethane solution to give the chlorinated product 13 rather than the expected tosylate 3 by a mechanism that could involve neighbouring group participation of the nitro-substituent. In contrast, the isomeric alcohol 15 reacted normally with 4-toluenesulfonyl chloride giving the tosylate 16 under similar conditions. J. Heterocyclic Chem., 42, 1215Chem., 42, (2005.We have recently reported the preparation of a series of 5,6-dihydrobenzimidazo[2,1-a]isoquinoline derivatives 6 [1] and their corresponding N-oxide derivatives 5 [1,2] as part of a study of analogues of the anti-cancer agent Ellipticine (1) and its 9-oxygenated derivatives (Scheme 1) [1]. N-Oxides 5 were readily prepared by cyclodehydration of 2-(2-nitroaryl)-1,2,3,4-tetrahydroisoquinolines 2 in boiling propionic acid (the t-amino effect) [3] and deoxygenation of these compounds with phosphorus trichloride yielded derivatives of heterocyle 6 [1]. We were also interested in the preparation of the fully conjugated benzimidazo[2,1-a]isoquinolines 7 but the attempted oxidation of derivatives of heterocycles 6 were unsuccessful. Literature precedence suggested that this transformation might not be readily achieved because 2,3,9,10-tetramethoxybenzimidazo[2,1-a]isoquinoline had only been obtained in 10 % yield by palladium on carbon mediated dehydrogenation of the corresponding 5,6-dihydroderivative [4]. An alternative approach to these fully conjugated heterocycles was therefore sought.The strategy we envisaged was to prepare the 4-toluenesulfonate derivative 3 from which the enamine 4a might be obtained by base-induced elimination. Tautomerisation of this enamine might be then expected to yield the 6-methyl derivative 8 of compound 7 (Scheme 1). This note describes an unexpected reaction of the 4-toluenesulfonate derivative 3.The synthetic route to the 4-toluenesulfonate derivative 3 is shown in Scheme 2. 1,2,3,4-Tetrahydroisoquinoline-3-carboxylic acid (9) was reacted with 2-fluoronitrobenzene (10) and the resulting carboxylic acid was esterified directly by treatment with dimethyl sulfate under basic conditions giving the ester 11. Reduction of ester 11 was achieved by treatment with lithium borohydride in the presence of trimethoxyborane yielding the alcohol 12 [5]. When the alcohol 12 was treated with 4-toluenesulfonyl chloride in pyridine, unexpectedly, the chloride 13 was obtained. The formation of the chloride 13 has been rationalised as shown in Scheme 2 in which neighbouring group participation by the nitro-group results in a favourable 7-endo-tet intramolecular reaction [6] giving a putative cyclic intermediate that is then attacked by chloride yielding the product 13. Compound 13 could also be prepared by an alternative route by the reaction of alcohol Sep-Oct 2005 1215

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Improved procedure for the asymmetric reduction of prochiral ketones by B-3-pinanyl-9-borabicyclo[3.3.1]nonane

Cited by 57 publications

References 0 publications

Accurate determinations of the extent to which the SE2? reactions of allyl-, allenyl- and propargylsilanes are stereospecifically anti

Accurate determinations of the extent to which the SE2? reactions of allyl-, allenyl- and propargylsilanes are stereospecifically anti

Synthesis of the North 1 Unit of the Cephalostatin Family from Hecogenin Acetate¹

Possible neighbouring group participation of a nitro-group in the conversion of 3-hydroxymethyl-2-(2-nitrophenyl)-1,2,3,4-tetrahydroisoquinoline into its 3-chloromethyl derivative

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Improved procedure for the asymmetric reduction of prochiral ketones by B-3-pinanyl-9-borabicyclo[3.3.1]nonane

Cited by 57 publications

References 0 publications

Accurate determinations of the extent to which the SE2? reactions of allyl-, allenyl- and propargylsilanes are stereospecifically anti

Accurate determinations of the extent to which the SE2? reactions of allyl-, allenyl- and propargylsilanes are stereospecifically anti

Synthesis of the North 1 Unit of the Cephalostatin Family from Hecogenin Acetate1

Possible neighbouring group participation of a nitro-group in the conversion of 3-hydroxymethyl-2-(2-nitrophenyl)-1,2,3,4-tetrahydroisoquinoline into its 3-chloromethyl derivative

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Synthesis of the North 1 Unit of the Cephalostatin Family from Hecogenin Acetate¹