The Experts below are selected from a list of 111 Experts worldwide ranked by ideXlab platform

Stephen J. Connon - One of the best experts on this subject based on the ideXlab platform.

  • base Challenges: Chemoselectivity and Enantioselectivity
    2016
    Co-Authors: Sarah E. O’toole, Christopher A. Rose, Sivaji Gundala, Kirsten Zeitler, Stephen J. Connon
    Abstract:

    Abstract: It has been shown for the first time that triazolium pre-catalysts promote (in the presence of base) highly chemoselective crossed Acyloin Condensation reactions between aliphatic and ortho-substituted aromatic aldehydes. An o-bromine atom can serve as a temporary directing group to ensure high chemoselectivity (regardless of the nature of the other substituents on the aromatic ring) which then can be conveniently removed. The process is of broad scope and is operationally simple as it does not require the pre-activation of any of the coupling partners to ensure selectivtiy. Preliminary data indicates that highly enantioselective variants of the reaction are feasible using chiral pre-catalysts. α-Hydroxy ketones are highly useful building blocks for the synthesis of heterocycles, natural products, agrochemicals and (inter alia1) pharmaceuticals.2 In addition, the unsymmetrical nature of the building block allows for access to other important synthetic precursors, such as chiral 1,2-diols and amino alcohols.3 As a consequence, the development of routes to these compounds via metal-catalysed heteroatom transfer4 and organocatalytic α-oxidation chemistry5 have been extensively investigated 2 recently.6 While these methods are undoubtedly useful, if one considers the power and utility of the aldol reaction7 as a C-C bonding forming process for the generation of β-hydroxy aldehydes/ketones, it is apparent that the organocatalytic direct coupling of two different aldehydes (if chemoselective) potentially offers a more modular and direct approach to the preparation of Acyloins than α-functionalization chemistry (Scheme 1A)

  • highly chemoselective direct crossed aliphatic aromatic Acyloin Condensations with triazolium derived carbene catalysts
    ChemInform, 2011
    Co-Authors: Sarah E Otoole, Christopher A. Rose, Sivaji Gundala, Kirsten Zeitler, Stephen J. Connon
    Abstract:

    In the presence of Rb2CO3 and the triazole TAC ortho-substituted aromatic aldehydes undergo efficient and highly chemoselective Acyloin Condensation with branched and unbranched aliphatic aldehydes to afford α-hydroxy ketones like (III), (V), and (VII).

  • highly chemoselective direct crossed aliphatic aromatic Acyloin Condensations with triazolium derived carbene catalysts
    Journal of Organic Chemistry, 2011
    Co-Authors: Sarah E Otoole, Christopher A. Rose, Sivaji Gundala, Kirsten Zeitler, Stephen J. Connon
    Abstract:

    It has been shown for the first time that triazolium precatalysts promote (in the presence of base) highly chemoselective crossed Acyloin Condensation reactions between aliphatic and ortho-substituted aromatic aldehydes. An o-bromine atom can serve as a temporary directing group to ensure high chemoselectivity (regardless of the nature of the other substituents on the aromatic ring) which then can be conveniently removed. The process is of broad scope and is operationally simple as it does not require the preactivation of any of the coupling partners to ensure selectivtiy. Preliminary data indicate that highly enantioselective variants of the reaction are feasible using chiral precatalysts.

Janice M. Nelke - One of the best experts on this subject based on the ideXlab platform.

  • the Acyloin Condensation
    Organic Reactions, 2011
    Co-Authors: Jordan J. Bloomfield, Dennis C. Owsley, Janice M. Nelke
    Abstract:

    The Acyloin Condensation usually involves the reductive dimerization of a carboxylic ester, although acid chlorides and the anhydrides have been used. The reducing agent is in an alkali metal and the product is an ene-diolate. Two gram-atoms of metal are required for each mole of ester with the concomitant formation of a mole of akoxide and one-half mole of the ene-diolate. Oxidation of Acyloins to diketoes can be accomplished by a variety of reagents. Acyloins can be reduced to ketones by various modifications of the Clemmenson technique. Under mild conditions the ketone will dominate. This chapter presents a complete picture of both the linear and cyclic Acyloin Condensation with particular emphasis on developments since 1960. The discussion is closely limited to the Acyloin Condensation and its modifications. Keywords: Condensation; Acyloin; dicarboxylic acids; monocarboxyl acids; reduction; oxalates; malonates; succinates; glutarates; adipates; pimelates; heterocyclic esters; esters; ketone; semidiones; experimental procedures

  • Acyloin Condensation in which chlorotrimethylsilane is used as a trapping agent 1 2 bis trimethylsilyloxy cyclobutene and 2 hydroxycyclobutanone
    Organic Syntheses, 2003
    Co-Authors: Jordan J. Bloomfield, Janice M. Nelke
    Abstract:

    Acyloin Condensation in which chlorotrimethylsilane is used as a trapping agent: 1,2-bis(trimethylsilyloxy)cyclobutene and 2-hydroxycyclobutanone product: 1,2-Bis(trimethylsilyloxy)cyclobutene product: 2-hydroxycyclobutanone Keywords: coupling; cyclization, reductive cyclization; reduction, miscellaneous; chlorotrimethylsilane, drying of; sodium sand; sodium-potassium alloy; toluene; chlorotrimethylsilane, in Acyloin reactions; sodium-potassium alloy; addition funnels, Hershberg; dry-box, in the preparation of 2-hydroxycyclobutanone; stirrers, vibromixer; vibromixer

Sarah E Otoole - One of the best experts on this subject based on the ideXlab platform.

Jordan J. Bloomfield - One of the best experts on this subject based on the ideXlab platform.

  • the Acyloin Condensation
    Organic Reactions, 2011
    Co-Authors: Jordan J. Bloomfield, Dennis C. Owsley, Janice M. Nelke
    Abstract:

    The Acyloin Condensation usually involves the reductive dimerization of a carboxylic ester, although acid chlorides and the anhydrides have been used. The reducing agent is in an alkali metal and the product is an ene-diolate. Two gram-atoms of metal are required for each mole of ester with the concomitant formation of a mole of akoxide and one-half mole of the ene-diolate. Oxidation of Acyloins to diketoes can be accomplished by a variety of reagents. Acyloins can be reduced to ketones by various modifications of the Clemmenson technique. Under mild conditions the ketone will dominate. This chapter presents a complete picture of both the linear and cyclic Acyloin Condensation with particular emphasis on developments since 1960. The discussion is closely limited to the Acyloin Condensation and its modifications. Keywords: Condensation; Acyloin; dicarboxylic acids; monocarboxyl acids; reduction; oxalates; malonates; succinates; glutarates; adipates; pimelates; heterocyclic esters; esters; ketone; semidiones; experimental procedures

  • Acyloin Condensation in which chlorotrimethylsilane is used as a trapping agent 1 2 bis trimethylsilyloxy cyclobutene and 2 hydroxycyclobutanone
    Organic Syntheses, 2003
    Co-Authors: Jordan J. Bloomfield, Janice M. Nelke
    Abstract:

    Acyloin Condensation in which chlorotrimethylsilane is used as a trapping agent: 1,2-bis(trimethylsilyloxy)cyclobutene and 2-hydroxycyclobutanone product: 1,2-Bis(trimethylsilyloxy)cyclobutene product: 2-hydroxycyclobutanone Keywords: coupling; cyclization, reductive cyclization; reduction, miscellaneous; chlorotrimethylsilane, drying of; sodium sand; sodium-potassium alloy; toluene; chlorotrimethylsilane, in Acyloin reactions; sodium-potassium alloy; addition funnels, Hershberg; dry-box, in the preparation of 2-hydroxycyclobutanone; stirrers, vibromixer; vibromixer

Sivaji Gundala - One of the best experts on this subject based on the ideXlab platform.

  • base Challenges: Chemoselectivity and Enantioselectivity
    2016
    Co-Authors: Sarah E. O’toole, Christopher A. Rose, Sivaji Gundala, Kirsten Zeitler, Stephen J. Connon
    Abstract:

    Abstract: It has been shown for the first time that triazolium pre-catalysts promote (in the presence of base) highly chemoselective crossed Acyloin Condensation reactions between aliphatic and ortho-substituted aromatic aldehydes. An o-bromine atom can serve as a temporary directing group to ensure high chemoselectivity (regardless of the nature of the other substituents on the aromatic ring) which then can be conveniently removed. The process is of broad scope and is operationally simple as it does not require the pre-activation of any of the coupling partners to ensure selectivtiy. Preliminary data indicates that highly enantioselective variants of the reaction are feasible using chiral pre-catalysts. α-Hydroxy ketones are highly useful building blocks for the synthesis of heterocycles, natural products, agrochemicals and (inter alia1) pharmaceuticals.2 In addition, the unsymmetrical nature of the building block allows for access to other important synthetic precursors, such as chiral 1,2-diols and amino alcohols.3 As a consequence, the development of routes to these compounds via metal-catalysed heteroatom transfer4 and organocatalytic α-oxidation chemistry5 have been extensively investigated 2 recently.6 While these methods are undoubtedly useful, if one considers the power and utility of the aldol reaction7 as a C-C bonding forming process for the generation of β-hydroxy aldehydes/ketones, it is apparent that the organocatalytic direct coupling of two different aldehydes (if chemoselective) potentially offers a more modular and direct approach to the preparation of Acyloins than α-functionalization chemistry (Scheme 1A)

  • highly chemoselective direct crossed aliphatic aromatic Acyloin Condensations with triazolium derived carbene catalysts
    ChemInform, 2011
    Co-Authors: Sarah E Otoole, Christopher A. Rose, Sivaji Gundala, Kirsten Zeitler, Stephen J. Connon
    Abstract:

    In the presence of Rb2CO3 and the triazole TAC ortho-substituted aromatic aldehydes undergo efficient and highly chemoselective Acyloin Condensation with branched and unbranched aliphatic aldehydes to afford α-hydroxy ketones like (III), (V), and (VII).

  • highly chemoselective direct crossed aliphatic aromatic Acyloin Condensations with triazolium derived carbene catalysts
    Journal of Organic Chemistry, 2011
    Co-Authors: Sarah E Otoole, Christopher A. Rose, Sivaji Gundala, Kirsten Zeitler, Stephen J. Connon
    Abstract:

    It has been shown for the first time that triazolium precatalysts promote (in the presence of base) highly chemoselective crossed Acyloin Condensation reactions between aliphatic and ortho-substituted aromatic aldehydes. An o-bromine atom can serve as a temporary directing group to ensure high chemoselectivity (regardless of the nature of the other substituents on the aromatic ring) which then can be conveniently removed. The process is of broad scope and is operationally simple as it does not require the preactivation of any of the coupling partners to ensure selectivtiy. Preliminary data indicate that highly enantioselective variants of the reaction are feasible using chiral precatalysts.