A new reagent for the determination of the optical purity of primary, secondary, and tertiary chiral alcohols and of thiols

Alexakis, Alexandre; Mutti, S.; Mangeney, Pierre

doi:10.1021/jo00030a034

“…[6] To establish the relative configuration and diastereomeric purity of 7, acid-and base-mediated eliminations as described by Hudrlik and Peterson were conducted with 7 f as a representative example (Scheme 3). [7] These remarkably stereospecific processes produced the corresponding cis and trans alkenes 8 f ( 1 H NMR: J = 10.7 and 15.8 Hz, respectively) and thus clearly revealed the absence of the anti diastereomer in 7 f. We also prepared 7 f independently as a mixture of diastereomers by using the 10-Ph analogue of 1 b and found that clearly resolved 13 C NMR spectroscopic signals were easily observed for the syn versus anti isomers; four clearly resolved signals were observed in the 31 P NMR spectrum of the mixture of the four esters derived from the isomers of 7 f by the protocol of Alexakis et al [8,9] To determine the absolute configuration of 7, we subjected 7 b to hydrogenation followed by base-mediated desilylation [10] of the saturated b-silyl alcohol to provide (À)-(4R)-octanol, whose configuration is known. The pre-transition-state complex A represents a convenient way to view the origin of the observed selectivity for this and related processes.…”

mentioning

confidence: 75%

“…The cold bath was removed 10 min after [a] The anti isomer was not detected by NMR spectroscopy for any of the alcohols 7. In the case of 7 f, stereospecific eliminations to give 8 f were carried out to confirm its high syn diastereomeric purity, which was verified by 31 P NMR spectroscopic analysis of a mixture of esters derived from the four isomers of this alcohol by the method of Alexakis et al [8] [b] The ee value of the product was determined by conversion into the Alexakis esters and analysis by 31 P NMR spectroscopy. [8] The products 7 a-c,e,f, of allenylboration at 25 8C were formed with 91, 98, 94, 98, and 94 % ee, respectively.…”

Section: Methodsmentioning

confidence: 99%

Asymmetric Synthesis of Isomerically Pure Allenyl Boranes from Alkynyl Boranes through a 1,2‐Insertion–1,3‐Borotropic Rearrangement

Canales

¹

,

González

²

,

Soderquist

³

2006

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Very recently, we described a variety of new 10-trimethylsilyl-9-borabicyclo[3.3.2]decane (10-TMS-9-BBD) reagents for the asymmetric allyl-, crotyl-, allenyl-, and propargylboration of aldehydes.[1] Prepared through adaptations of known organoborane transformations, these rigid and robust trialkyl borane systems are exceptionally stable and selective. Moreover, the related 10-Ph-9-BBD reagents, which are quite effective for the related addition reactions to ketones and ketimines, can also be prepared readily. [2] Simple Grignard procedures can be used to prepare many of these reagents, including the B-alkynyl 10-TMS-9-BBDs (2), the asymmetric Michael addition of which to N-acyl aldimines provides nonracemic N-propargyl amides.[3] On the basis of modeling studies with 2, we envisaged the highly stereoselective insertion of TMSCHN 2 into the alkynyl BÀC bond of 2 to give 4 via 3 (Scheme 1). An antiperiplanar 1,2-alkynyl migration (Matteson-type homologation) [4a] followed by a sterically driven suprafacial 1,3-borotropic rearrangement were expected to proceed with a minimum of TMS-TMS repulsions and ultimately convert the propargyl borane 4 into the novel chiral allenyl borane 1. [1c, 2a, 4b] The thermally stable, optically pure alkynyl boranes 2 (a: R = Me; b: R = (CH 2 ) 4 Cl; c: R = c-Pr; c-Pr = cyclopropyl) are readily prepared in either enantiomeric form through the reaction of the corresponding alkynyl Grignard reagents with the pseudoephedrine complexes 6 (96-99 %). At room temperature, TMSCHN 2 reacts cleanly with 2 with the evolution of nitrogen to form 1 ( 11 B NMR: d = 78 ppm) in 3 h. We view this process as occurring through the reversible addition of TMSCHN 2 to the least hindered side of 2, followed by the insertion of CHTMS into 2 with inversion. The chiral a-borylallenes 1 are then produced in enantiomerically and diastereomerically pure form in essentially quantitative yield by a suprafacial 1,3-borotropic rearrangement (Scheme 1).Asymmetric allenylboration [1b, 2c, 5] is a highly useful organoborane transformation. Compound 1 was tested as an asymmetric allenylboration reagent with representative aldehydes (Scheme 2). The addition was rapid at À78 8C (3 h), and the intermediate borinic esters 5 produced were either oxidized or converted into the pseudoephedrine complexes 6 for recycling back to 2 by the Grignard methodology. The syn b-TMS homopropargylic alcohols 7 were isolated in 80-96 % yield with d.r. 99:1 and 94-99 % ee (Table 1). This process is more enantioselective than allenylboration with the parent B-allenyl system (93-95 % ee).[1b] The enhanced enantioselectivity can be attributed to the additional a substituent Scheme 1. The preparation of 1 from 2 through insertion-borotropic rearrangement. TMS = trimethylsilyl.Scheme 2. Asymmetric allenylboration with 1.

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“…These compounds were cleanly prepared in a one-pot process by the sequential treatment of the corresponding allylic alcohols with the phospholidine 8, [9] as described by Alexakis et al, [10] followed by tosyl azide and diphenylphosphoryl azide (DPPA), [11] respectively (Table 1). [12] The reaction was monitored by 31 P NMR spectroscopy to ensure complete conversion of the intermediate phosphoramidite (d % 130 ppm for 2, whereas d % 24 ppm for 6 and d % 24 and À10 ppm for 7).…”

mentioning

confidence: 99%

Palladium‐Catalyzed [3,3] Sigmatropic Rearrangement of (Allyloxy)iminodiazaphospholidines: Allylic Transposition of CO and CN Functionality

Lee

¹

,

Batey

²

2004

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The principle of driving reactions thermodynamically through the conversion of P III reagents into P V =O products is well established, as exemplified by the Wittig and Mitsunobu reactions, and the [2,3] sigmatropic rearrangement of allyl phosphites into allyl phosphonates.[1] Herein we describe a novel [3,3] sigmatropic rearrangement in which allylic transposition is driven by a P V = N to P V = O interconversion (Scheme 1). We envisaged a process whereby conversion of an allylic alcohol 1 into a phosphoramidite 2, followed by a Staudinger reaction [2] would generate a phospholidine 3. A [3,3] sigmatropic 3-aza-2-phospha-1-oxa-Cope [3] rearrangement of 3 would then generate a phosphoramide 4, which on deprotection would lead to the transposed allylic amine 5.[4]The overall process is analogous to the aza variants of the Cope [3,3] sigmatropic rearrangement, [5] the most important example of which is the well-known Overman rearrangement of allylic imidates into allylic amides.[6] The estimated thermodynamic driving force for a phospholidine-phosphoramide interconversion, [7] such as would occur in a sigmatropic rearrangement, is approximately 25 kcal mol À1 .[8]The feasibility of this approach was tested by using (allyloxy)iminodiazaphospholidines 6 and 7 as substrates.

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“…In the case of 7 f, stereospecific eliminations to give 8 f were carried out to confirm its high syn diastereomeric purity, which was verified by 31 P NMR spectroscopic analysis of a mixture of esters derived from the four isomers of this alcohol by the method of Alexakis et al [8] [b] The ee value of the product was determined by conversion into the Alexakis esters and analysis by 31 P NMR spectroscopy. [8] The products 7 a-c,e,f, of allenylboration at 25 8C were formed with 91, 98, 94, 98, and 94 % ee, respectively. Zuschriften 402 www.angewandte.de the addition, and the solution was concentrated under vacuum by using standard techniques to prevent the exposure of the borane to the open atmosphere.…”

Section: Methodsmentioning

confidence: 99%

Asymmetric Synthesis of Isomerically Pure Allenyl Boranes from Alkynyl Boranes through a 1,2‐Insertion–1,3‐Borotropic Rearrangement

Canales¹,

González²,

Soderquist³

2006

View full text Add to dashboard Cite

Very recently, we described a variety of new 10-trimethylsilyl-9-borabicyclo[3.3.2]decane (10-TMS-9-BBD) reagents for the asymmetric allyl-, crotyl-, allenyl-, and propargylboration of aldehydes.[1] Prepared through adaptations of known organoborane transformations, these rigid and robust trialkyl borane systems are exceptionally stable and selective. Moreover, the related 10-Ph-9-BBD reagents, which are quite effective for the related addition reactions to ketones and ketimines, can also be prepared readily. [2] Simple Grignard procedures can be used to prepare many of these reagents, including the B-alkynyl 10-TMS-9-BBDs (2), the asymmetric Michael addition of which to N-acyl aldimines provides nonracemic N-propargyl amides.[3] On the basis of modeling studies with 2, we envisaged the highly stereoselective insertion of TMSCHN 2 into the alkynyl BÀC bond of 2 to give 4 via 3 (Scheme 1). An antiperiplanar 1,2-alkynyl migration (Matteson-type homologation) [4a] followed by a sterically driven suprafacial 1,3-borotropic rearrangement were expected to proceed with a minimum of TMS-TMS repulsions and ultimately convert the propargyl borane 4 into the novel chiral allenyl borane 1. [1c, 2a, 4b] The thermally stable, optically pure alkynyl boranes 2 (a: R = Me; b: R = (CH 2 ) 4 Cl; c: R = c-Pr; c-Pr = cyclopropyl) are readily prepared in either enantiomeric form through the reaction of the corresponding alkynyl Grignard reagents with the pseudoephedrine complexes 6 (96-99 %). At room temperature, TMSCHN 2 reacts cleanly with 2 with the evolution of nitrogen to form 1 ( 11 B NMR: d = 78 ppm) in 3 h. We view this process as occurring through the reversible addition of TMSCHN 2 to the least hindered side of 2, followed by the insertion of CHTMS into 2 with inversion. The chiral a-borylallenes 1 are then produced in enantiomerically and diastereomerically pure form in essentially quantitative yield by a suprafacial 1,3-borotropic rearrangement (Scheme 1).Asymmetric allenylboration [1b, 2c, 5] is a highly useful organoborane transformation. Compound 1 was tested as an asymmetric allenylboration reagent with representative aldehydes (Scheme 2). The addition was rapid at À78 8C (3 h), and the intermediate borinic esters 5 produced were either oxidized or converted into the pseudoephedrine complexes 6 for recycling back to 2 by the Grignard methodology. The syn b-TMS homopropargylic alcohols 7 were isolated in 80-96 % yield with d.r. 99:1 and 94-99 % ee (Table 1). This process is more enantioselective than allenylboration with the parent B-allenyl system (93-95 % ee).[1b] The enhanced enantioselectivity can be attributed to the additional a substituent Scheme 1. The preparation of 1 from 2 through insertion-borotropic rearrangement. TMS = trimethylsilyl.Scheme 2. Asymmetric allenylboration with 1.

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A new reagent for the determination of the optical purity of primary, secondary, and tertiary chiral alcohols and of thiols

Cited by 121 publications

References 0 publications

Asymmetric Synthesis of Isomerically Pure Allenyl Boranes from Alkynyl Boranes through a 1,2‐Insertion–1,3‐Borotropic Rearrangement

Asymmetric Synthesis of Isomerically Pure Allenyl Boranes from Alkynyl Boranes through a 1,2‐Insertion–1,3‐Borotropic Rearrangement

Palladium‐Catalyzed [3,3] Sigmatropic Rearrangement of (Allyloxy)iminodiazaphospholidines: Allylic Transposition of CO and CN Functionality

Asymmetric Synthesis of Isomerically Pure Allenyl Boranes from Alkynyl Boranes through a 1,2‐Insertion–1,3‐Borotropic Rearrangement

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