<i>Anti</i>-Selective Glycolate Aldol Additions with an Oxapyrone Boron Enolate

Andrus, Merritt B.; Sekhar, B. B. V. Soma; Meredith, and Erik L.; Dalley, N. Kent

doi:10.1021/ol0002166

Cited by 80 publications

(32 citation statements)

References 38 publications

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“…[3][4][5][6][7][8] In addition, they often suffered from a narrow substrate scope, low yields, and low stereoselectivities. [2] Furthermore, 1,2-diols can serve as valuable synthetic precursors for the construction of a wide variety of other useful structures.…”

mentioning

confidence: 99%

Cross‐Metathesis/Iridium(I)‐catalyzed Allylic Etherification Strategy: (Iterative) Catalytic Asymmetric Synthesis of syn‐ and anti‐1,2‐Diols

Kim¹,

Lee²,

Kong³

et al. 2013

Angew Chem Int Ed

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1,2-Diol functional groups are common structures in many biologically active natural products [1] and "privileged" chiral catalysts/ligands. [2] Furthermore, 1,2-diols can serve as valuable synthetic precursors for the construction of a wide variety of other useful structures. 1,2-Diols can appear in many different forms depending on their protection state (diprotected, monoprotected, or free diol), as well as their absolute and relative stereochemistry (syn or anti). Thus, an ideal synthetic method/strategy for 1,2-diols would be one that can a) furnish any of the aforementioned 1,2-diol forms and b) control their absolute and relative stereochemistry by using a pair of enantiomeric ligands/catalysts, but such methodology is not currently available.Despite tremendous methodological advancements, literature inspection surprisingly revealed that almost all prior asymmetric methods for the synthesis of 1,2-diols focused on controlling relative stereochemistry of 1,2-diols, thus giving either syn-or anti-1,2-diols, and employed chiral reagents and auxiliaries for stereochemical control. [3][4][5][6][7][8] In addition, they often suffered from a narrow substrate scope, low yields, and low stereoselectivities. To our knowledge, the only catalytic asymmetric method that met the above two criteria was recently reported by the McQuade group, who employed the copper-catalyzed asymmetric allylic boronation/cross-metathesis (AAB/CM) strategy. [9] Although highly selective formation of differentiated syn-and anti-1,2-diols could be achieved by using a pair of enantiomeric ligands, the strategy required two extra steps for the in situ oxidation of the boronate product of the AAB reaction and the subsequent alcohol protection, and the AAB reaction did not occur with a TBS protecting group, thus considerably limiting the generality and practicality of the strategy.In recent years, iridium(I)-catalyzed allylic substitution reactions have emerged as a powerful tool for the enantioselective introduction of carbon-carbon and carbon-heteroatom bonds. [10] A distinct feature of iridium(I)-catalyzed allylic substitution reactions is the formation of chiral branched allylation products from achiral linear allyl sub-strates, which complements the more traditional palladiumcatalyzed allylic substitution reactions which typically give rise to linear allylation products. [11] Iridium-catalyzed allylic etherification reactions have been shown to generate a wide range of protected and free chiral allylic alcohols in high yields at synthetically useful levels of stereoselectivity [Eq. (1); PG = protecting group]. [12] We recently demonstrated that iridium(I)-catalyzed decarboxylative allylic etherification exhibited much broader substrate scope and higher reaction yield than the corresponding intermolecular version, and that stereoselection in iridium(I)-catalyzed diastereoselective decarboxylative allylic etherification was controlled by the ligands/catalysts used [Eq.(2); PMP = p-methoxyphenyl]. [13] Based on these results, we envision...

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confidence: 99%

Cross‐Metathesis/Iridium(I)‐catalyzed Allylic Etherification Strategy: (Iterative) Catalytic Asymmetric Synthesis of syn‐ and anti‐1,2‐Diols

Kim¹,

Lee²,

Kong³

et al. 2013

Angew Chem Int Ed

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“…13 In this work, the hydrobenzoin-derived pyrone 41 was synthesized in order to constrain the geometry of the boron enolate formed through its reaction with (cyclohexyl) 2 When the ortho-functionalized hydrobenzoin auxiliaries were employed in these reactions a decrease in selectivity or yield was observed. Thus, reaction of isobutyraldehyde with the ortho-substituted auxiliary 41a gave an improved yield (91%) but a decrease in diastereoselectivity (42a:43a = 9:1 …”

Section: Hydrobenzoin As An Auxiliary In Anti-selective Glycolate Aldmentioning

confidence: 99%

“…(Table 6, entry 1). As 176 and 177 (Table 6) proved to be indistinguishable by 1 H, 13 C, or 2 D-NMR, the deuterium incorporation was calculated from integration of the 1 H NMR spectra of crude reaction products using formula 3 ( Figure 9):…”

Section: Ortho-metalation Reactions Involving a Benzyl Alcohol Or α-Mmentioning

confidence: 99%

Bidirectional Metalation of Hydrobenzoin: Direct Access to New Chiral Ligands and Auxiliaries

2009

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“…Several recent publications have featured natural products that incorporate this moiety into their synthesis, including thapsigarin, viridiofungin, zaragozic acid, and fukinolic acid (Scheme 1). 3-6 Given the prevalence of α-hydroxy acids in small molecules, new synthetic methods for their synthesis are desirable 7-13. We recently reported the development of a method to obtain α-hydroxy acids from simple α-keto esters utilizing metal-catalyzed silylene transfer 14.…”

Section: Introductionmentioning

confidence: 99%

Silylene transfer to α-keto esters and application to the synthesis of γ-lactones

Howard¹,

Woerpel²

2009

Tetrahedron

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Anti-Selective Glycolate Aldol Additions with an Oxapyrone Boron Enolate

Cited by 80 publications

References 38 publications

Cross‐Metathesis/Iridium(I)‐catalyzed Allylic Etherification Strategy: (Iterative) Catalytic Asymmetric Synthesis of syn‐ and anti‐1,2‐Diols

Cross‐Metathesis/Iridium(I)‐catalyzed Allylic Etherification Strategy: (Iterative) Catalytic Asymmetric Synthesis of syn‐ and anti‐1,2‐Diols

Bidirectional Metalation of Hydrobenzoin: Direct Access to New Chiral Ligands and Auxiliaries

Silylene transfer to α-keto esters and application to the synthesis of γ-lactones

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