Hydride as a leaving group in the reaction of pinacolborane with halides under ambient Grignard and Barbier conditions. One-pot synthesis of alkyl, aryl, heteroaryl, vinyl, and allyl pinacolboronic esters
Autor: | Bakthan Singaram, Terry J. Rettenmaier, W. Todd Wipke, Rachel Snelling, Whitney Bryks, Jesse Banwell, Jacob W. Clary |
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Rok vydání: | 2011 |
Předmět: |
Allylic rearrangement
Molecular Structure Hydride Magnesium Organic Chemistry Magnesium hydride chemistry.chemical_element Esters Stereoisomerism Medicinal chemistry Boronic Acids chemistry.chemical_compound Halogens chemistry Bromide Reagent Magnesium bromide Organometallic Compounds Organic chemistry Boranes Tetrahydrofuran Hydrogen |
Zdroj: | The Journal of organic chemistry. 76(23) |
ISSN: | 1520-6904 |
Popis: | Grignard reagents (aliphatic, aromatic, heteroaromatic, vinyl, or allylic) react with 1 equiv of 4,4,5,5-tetramethyl-1,3,2-dioxaborolane (pinacolborane, PinBH) at ambient temperature in tetrahydrofuran (THF) to afford the corresponding pinacolboronates. The initially formed dialkoxy alkylborohydride intermediate quickly eliminates hydridomagnesium bromide (HMgBr) and affords the product boronic ester in very good yield. Hydridomagnesium bromide (HMgBr) in turn disproportionates to a 1:1 mixture of magnesium hydride (MgH(2)) and magnesium bromide (MgBr(2)) on addition of pentane to the reaction mixture. DFT calculations (Gaussian09) at the B3LYP/6-31G(d) level of theory show that disproportionation of HMgBr to MgH(2) and MgBr(2) is viable in the coordinating ethereal solvents. This reaction also can be carried out under Barbier conditions, where the neat PinBH is added to the flask prior to the in situ formation of Grignard reagent from the corresponding organic halide and magnesium metal. Pinacolboronic ester synthesis under Barbier conditions does not give Wurtz coupling side products from reactive halides, such as benzylic and allylic halides. The reaction between PinBH and various Grignard reagents is an efficient, mild, and general method for the synthesis of pinacolboronates. |
Databáze: | OpenAIRE |
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