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Abstract
(Z)-1-Bromo-1-alkenylboronate esters were easily synthesized from the hydroboration of terminal alkynes with dibromoborane dimethyl complex under nitrogen atmosphere followed by treatment with propne-1,3-diol. These boronate esters are readily reacted with 1,3-dioxan-2-ylethyl)magnesium bromide in ether and tetrahydrofuran at -78 ºC for 1 h. The resulting "ate" complex upon addition of sodium methoxide in methanol undergo intramolecular nucleophilic substitution reactions to produce the corresponding (E)-alkenylboronate esters containing (1,3-dioxan-2-ylethyl) moiety in 70-82% isolated yields. The resulting intermediates are oxidized with sodium acetate and hydrogen peroxide to provide the corresponding β-keto cycloacetals in good yields (68-84%).
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References
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- H.C. Brown, T. Imai and N.G. Bhat, Vinylic Organoboranes. 7. Stereoselective Synthesis of (E)-(1-Substituted-1-alkenyl)boronic Esters by the Nucleophilic Substitution of (Z)-(1-Bromo-1-alkenyl)-boronic Esters with Organolithium or Grignard Reagents. Isolation and Oxidation to Ketones, J. Org. Chem., 51, 5277 (1986); https://doi.org/10.1021/jo00376a042
- H.C. Brown and R. Soundararajan, A Convenient Synthesis of b,g-Unsaturated Ketones via Allylation of Z-1-Halo-1-alkenyl-1,3,2-dioxaborolane, Tetrahedron Lett., 35, 6963 (1994); https://doi.org/10.1016/0040-4039(94)88199-5
- N.G. Bhat, C. Martinez and J. De Los Santos, A Novel Synthesis of b-Ketosilanes via Organoboranes, Tetrahedron Lett., 41, 6541 (2000); https://doi.org/10.1016/S0040-4039(00)01088-1
References
N.D. Bartolo and K.A. Woerpel, Mechanistic Insight into Additions of Allylic Grignard Reagents to Carbonyl Compounds, J. Org. Chem., 83, 10197 (2018); https://doi.org/10.1021/acs.joc.8b01430
H.C. Brown, N.G. Bhat and V. Somayaji, Organoboranes. 30. Convenient Procedures for the Synthesis of Alkyl- and Alkenylboronic Acids and Esters, Organometallics, 2, 1311 (1983); https://doi.org/10.1021/om50004a008
D.S. Matteson and D. Majumdar, Homologation of Boronic Esters to a-Chloro Boronic Esters, Organometallics, 2, 1529 (1983); https://doi.org/10.1021/om50005a008
D.J.S. Tsai, P.K. Jesthi and D.S. Matteson, Diastereoselection in Reactions of Pinanediol Dichloromethaneboronate, Organometallics, 2, 1543 (1983); https://doi.org/10.1021/om50005a010
H.C. Brown, N.R. De Lue, Y. Yamamoto, K. Maruyama, T. Kasahara, S. Murahashi and A. Sonoda, Organoboranes. 23. Reaction of Organo-lithium and Grignard Reagents with a-Bromoalkylboronate Esters. A Convenient, Essentially Quantitative Procedure for the Synthesis of Tertiary Alkyl-, Benzyl-, Propargyl- and Stereospecific Allylboranes, J. Org. Chem., 42, 4088 (1977); https://doi.org/10.1021/jo00445a022
M.W. Rathke, E. Chao and G. Wu, The Preparation and Reactions of Esters of Dichloromethaneboronic Acid, J. Organomet. Chem., 122, 145 (1976); https://doi.org/10.1016/S0022-328X(00)80606-3
H.C. Brown and T. Imai, Organoboranes. 37. Synthesis and Properties of (Z)-1-Alkenylboronic Esters, Organometallics, 3, 1293 (1984); https://doi.org/10.1021/om00087a013
H.C. Brown, T. Imai and N.G. Bhat, Vinylic Organoboranes. 7. Stereoselective Synthesis of (E)-(1-Substituted-1-alkenyl)boronic Esters by the Nucleophilic Substitution of (Z)-(1-Bromo-1-alkenyl)-boronic Esters with Organolithium or Grignard Reagents. Isolation and Oxidation to Ketones, J. Org. Chem., 51, 5277 (1986); https://doi.org/10.1021/jo00376a042
H.C. Brown and R. Soundararajan, A Convenient Synthesis of b,g-Unsaturated Ketones via Allylation of Z-1-Halo-1-alkenyl-1,3,2-dioxaborolane, Tetrahedron Lett., 35, 6963 (1994); https://doi.org/10.1016/0040-4039(94)88199-5
N.G. Bhat, C. Martinez and J. De Los Santos, A Novel Synthesis of b-Ketosilanes via Organoboranes, Tetrahedron Lett., 41, 6541 (2000); https://doi.org/10.1016/S0040-4039(00)01088-1