Stereocontrolled functionalization in the cyclohexane ring using organomolybdenum chemistry

Pearson, Anthony J.; Khan, M. Nazrul I.; Clardy, Jon; He, Chao

doi:10.1021/ja00295a030

Cited by 76 publications

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“…Lactone 11 was readily dehalogenated 23 (Zn/AcOH; 85%) to the known compound 12. 24 The use of conjugated dienes in ATRC reactions 25 is also feasible using carbene 1 as a catalyst as demonstrated by the cyclisation of the sorbyl ester 13 to the lactone 14. Lactone 14 was isolated as a single diastereoisomer in 46% yield.…”

Section: Methodsmentioning

confidence: 99%

Atom Transfer Radical Cyclisations Mediated by the Grubbs Ruthenium Metathesis Catalyst

Quayle¹,

Fengas²,

Richards³

2003

Synlett

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Section: Methodsmentioning

confidence: 99%

Atom Transfer Radical Cyclisations Mediated by the Grubbs Ruthenium Metathesis Catalyst

Quayle¹,

Fengas²,

Richards³

2003

Synlett

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“…For example, treatment of 7 , 10 , 11 , and 14 with NaH in DMSO in the presence of a catalytic amount of copper(II) 2-ethylhexanoate7 open to air provided the annulations products 17 – 20 in 83–92% isolated yields (Table 2). In earlier work, Pearson used different non-basic annulative demetalation reagents such as I 2 8 or NOBF 4 9 for related transformations, but exposing our substrates to these reagents (as well as prolonged standing in CDCl 3 ) yielded only the undesired elimination product (i.e., 16 , Scheme 2) through ionization of the carbon nucleophile10 and subsequent proton loss. Mechanistically, we suggest that the reactions of Table 2 proceed through 1-electron oxidation of the stabilized enolate to a radical11 that then reacts with the adjacent η 3 -allylmolybdenum moiety.…”

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confidence: 99%

A New Reaction Motif: “Homo-S_N2′-Like” Direct Nucleophilic Addition to Neutral η³-Allylmolybdenum Complexes. Total Synthesis of the Antimalarial (+)-Isofebrifugine

Chen

Liebeskind

2009

J. Am. Chem. Soc.

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Charge neutral TpMo(CO) 2 (5-acyloxy-η 3 -pyranyl) and TpMo(CO) 2 (5-acyloxy-η 3 -pyridinyl) scaffolds undergo a novel intermolecular "homo-S N 2′-like" reaction with a variety of carbon nucleophiles. Combined with an annulative demetalation, the homo-S N 2′-like substitution/annulative demetalation sequence rapidly generates 2,7-dioxabicyclo[4.3.0]nonane and 2-aza-7-oxabicyclo [4.3.0]nonane frameworks in good to excellent yields with high enantiopurity. An enantiocontrolled total synthesis of the antimalarial alkaloid (+)-isofebrifugine was achieved utilizing this reaction cascade.Enantiomerically pure, air and moisture-stable TpMo(CO) 2 (η 3 -pyranyl) and TpMo(CO) 2 (η 3 -pyridinyl) complexes, 1 and 2 (Scheme 1), are powerful scaffolds for the enantiocontrolled construction of substituted heterocycles.1 Readily available in multigram quantities, 1m they provide not only new bond construction strategies to access a variety of natural products, but they also constitute platforms from which to explore novel reactivity. A survey of the literature shows that a TpMo(CO) 2 -stabilized carbocation is a requisite intermediate in almost all synthetic transformations of the scaffolds.1a-i,1k,l,1n It was only recently that a new, noncationic pathway taking place through the direct nucleophilic addition of an internal enolate chemLL1@emory.edu. Supporting Information Available: Experimental procedures, synthesis and characterization of all new compounds and X-ray crystallographic studies of 8 (55 pages), scanned copies of 1 H and 13 C NMR spectra of all new compounds (64 pages). This material is available free of charge via the Internet at http://pubs.acs.org. to a terminal π-carbon of neutral 5-oxo-η 3 -pyranyl (and pyridinyl) moiety was reported.1j,1o This synthetically useful 1,5-Michael-like functionalization mode was explained, in part, by the tendency of TpMo(CO) 2 systems to favor 6-coordinate over 7-coordinate structures, 2 and also because the nucleophilic addition generates a characterizable anionic TpMo(CO) 2 intermediate (5 in Scheme 1), which possesses three good π-back-bonding ligands to delocalize the anionic charge: 2 terminal CO's and the η 2 -enone ligand. These observations led us to wonder if the preference for 6-coordinate over 7-coordinate structures alone would be sufficient to enhance a more general nucleophilic addition pathway by which TpMo(CO) 2 (η 3 -allyl) systems that are less-activated than the 5-oxo-η 3 -pyranyl/pyridinyl complexes could be functionalized. Following these considerations, we report herein the first examples of the "homo-S N 2′-like" intermolecular nucleophilic substitution of charge neutral TpMo(CO) 2 (5-acyloxy-η 3 -pyranyl) and TpMo(CO) 2 (5-acyloxy-η 3 -pyridinyl) complexes (3 and 4, Scheme 1). This mechanistically new enantiocontrolled carbon-carbon bond forming reaction occurs enantiospecifically with excellent anti stereoselectivity. NIH Public AccessThe requisite substrates 3a-c, 4a,b (Table 1) are prepared in high yields from the readily available TpMo(CO) 2 (...

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“…The NN-stretching mode in the azide adduct [NBu 4 ][N 3 -1] (ṽ = 2137 cm À 1 ) is blue-shifted by 137 cm À 1 compared to free tetrabutylammonium azide. [23] A less distinct blue shift was observed in the literature know adduct [C 30 H 48 N 4 Sb 2 ][N 3 -B(C 6 F 5 ) 3 ] 2 (ṽ = 2123 cm À 1 ), [24] and Scheme 1. a) Synthesis of polymeric [1] n as a source of "donor free" 1 and b) synthesis of anionic silicates considered in this study. TfO [c] À 105.9 À 99.9 (À 134.5)…”

Section: Resultsmentioning

confidence: 86%

Synthesis and Characterization of Hypercoordinated Silicon Anions: Catching Intermediates of Lewis Base Catalysis

et al. 2022

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Anionic hypercoordinated silicates with weak donors were proposed as key intermediates in numerous silicon‐based reactions. However, their short‐lived nature rendered even spectroscopic observations highly challenging. Here, we characterize hypercoordinated silicon anions, including the first bromido‐, iodido‐, formato‐, acetato‐, triflato‐ and sulfato‐silicates. This is enabled by a new, donor‐free polymeric form of Lewis superacidic bis(perchlorocatecholato)silane 1. Spectroscopic, structural, and computational insights allow a reassessment of Gutmann's empirical rules for the role of silicon hypercoordination in synthesis and catalysis. The electronic perturbations of 1 exerted on the bound anions indicate pronounced substrate activation.

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Stereocontrolled functionalization in the cyclohexane ring using organomolybdenum chemistry

Cited by 76 publications

References 0 publications

Atom Transfer Radical Cyclisations Mediated by the Grubbs Ruthenium Metathesis Catalyst

Atom Transfer Radical Cyclisations Mediated by the Grubbs Ruthenium Metathesis Catalyst

A New Reaction Motif: “Homo-S_N2′-Like” Direct Nucleophilic Addition to Neutral η³-Allylmolybdenum Complexes. Total Synthesis of the Antimalarial (+)-Isofebrifugine

Synthesis and Characterization of Hypercoordinated Silicon Anions: Catching Intermediates of Lewis Base Catalysis

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Stereocontrolled functionalization in the cyclohexane ring using organomolybdenum chemistry

Cited by 76 publications

References 0 publications

Atom Transfer Radical Cyclisations Mediated by the Grubbs Ruthenium Metathesis Catalyst

Atom Transfer Radical Cyclisations Mediated by the Grubbs Ruthenium Metathesis Catalyst

A New Reaction Motif: “Homo-SN2′-Like” Direct Nucleophilic Addition to Neutral η3-Allylmolybdenum Complexes. Total Synthesis of the Antimalarial (+)-Isofebrifugine

Synthesis and Characterization of Hypercoordinated Silicon Anions: Catching Intermediates of Lewis Base Catalysis

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A New Reaction Motif: “Homo-S_N2′-Like” Direct Nucleophilic Addition to Neutral η³-Allylmolybdenum Complexes. Total Synthesis of the Antimalarial (+)-Isofebrifugine