Protodesilylation reactions of simple .beta.-hydroxysilanes (and .alpha.-hydroxysilanes). Homo-Brook rearrangements

Hudrlik, Paul F.; Hudrlik, Anne M.; Kulkarni, Ashok K.

doi:10.1021/ja00388a069

Cited by 128 publications

(39 citation statements)

References 3 publications

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“…The first of these goals was met by treatment with KO t -Bu/18-crown-6 – a procedure known to effect hydroxyl-directed desilylation. 18 Next, treatment with thiocarbonyldiimidazole furnished the functionalized azatricyclododecene 16 in 59% yield (over two steps). 18 Deoxygenation by treatment with tributyltin hydride and AIBN 19 was followed by acid-mediated alkene isomerization to deliver (−) -205B in 61% yield.…”

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confidence: 99%

Synthesis of Alkaloid (−)-205B via Stereoselective Reductive Cross-Coupling and Intramolecular [3+2] Cycloaddition

Yang

Micalizio

2012

J. Am. Chem. Soc.

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An asymmetric synthesis of alkaloid (−)-205B, a tricyclic member of the architecturally diverse family of natural products isolated from the skin of neotropical poison frogs, is described that proceeds through two recently developed stereoselective synthetic methods: (1) Ti-mediated allylic alcohol–imine reductive cross-coupling, and (2) intramolecular [3+2] cycloaddition of a glyoxylate-based homoallylic nitrone. The utility of this latter cycloaddition process for the assembly of the stereochemically dense piperidine core of 205B is noteworthy, as this method enables direct [3+2] annulation of an intermediate homoallylic (E)-nitrone via a pathway that is stereochemically unscathed by competitive [3,3] sigmatropic rearrangement processes. Overall, the synthesis is asymmetric, concise, and highly stereoselective – features which point to the potential future utility of these chemical methods in natural product synthesis and medicinal chemistry.

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confidence: 99%

Synthesis of Alkaloid (−)-205B via Stereoselective Reductive Cross-Coupling and Intramolecular [3+2] Cycloaddition

Yang

Micalizio

2012

J. Am. Chem. Soc.

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“…Proteodesilylation of α-hydroxy silylenones12,13 and site-selective eliminative opening of silyl substituted epoxides are known 14,15. We examined this type of elimination for spirodiepoxides derived from 5 , 14 and 15 (Table 2).…”

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Silyl-Substituted Spirodiepoxides: Stereoselective Formation and Regioselective Opening

et al. 2009

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“…[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.…”

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

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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Protodesilylation reactions of simple .beta.-hydroxysilanes (and .alpha.-hydroxysilanes). Homo-Brook rearrangements

Cited by 128 publications

References 3 publications

Synthesis of Alkaloid (−)-205B via Stereoselective Reductive Cross-Coupling and Intramolecular [3+2] Cycloaddition

Synthesis of Alkaloid (−)-205B via Stereoselective Reductive Cross-Coupling and Intramolecular [3+2] Cycloaddition

Silyl-Substituted Spirodiepoxides: Stereoselective Formation and Regioselective Opening

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

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