- Rationally improved chiral Bronsted acid for catalytic enantioselective allylboration of aldehydes with an expanded reagent scope
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(Chemical Equation Presented) One of the most useful reactions in organic synthesis, the stereocontrolled addition of allylic metal reagents to carbonyl compounds, provides access to enantiomerically enriched homoallylic alcohols related to the acetate, propionate, and other oxygen-containing functionalities present in a large number of biologically active natural products and pharmaceutical drugs. In the search for an ideal carbonyl allylation methodology, the catalytic enantioselective allylboration presents numerous advantages such as a high chemo-, diastereo-, and enantiocontrol with stable and nontoxic pinacol allylic boronates. This article reports a rationally improved diol·SnCl4 complex as chiral protic acid catalyst, which provides unprecedented levels of enantioselectivity in the catalytic allylation, methallylation, crotylation, and 2-bromoallylation of aliphatic aldehydes. The new diol, p-F-Vivol (4b), enables a more active diol·SnCl4 catalyst that can compete more effectively with the background uncatalyzed allylboration. The usefulness of this optimized catalytic allylboration methodology was demonstrated with an efficient synthesis of the naturally occurring pyranone (+)-dodoneine and to the preparation of biologically important exomethylene-γ-lactones.
- Rauniyar, Vivek,Hall, Dennis G.
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supporting information; experimental part
p. 4236 - 4241
(2009/09/30)
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- Pesticidal method using 2-phenylimidazole derivatives
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The invention provides a method for the control of arthropod, plant nematode, helminth or protozoan pests using a 2-phenylimidazole derivative of the formula: STR1 wherein R1 represents hydrogen, alkyl (optionally substituted by alkoxy, alkylthio, alkylsulphinyl, alkylsulphonyl, cyano, carboxy or alkoxycarbonyl), R2 and R3, each represents hydrogen, halogen, nitro, carboxy, cyano, alkoxycarbonyl, alkanoyl, or optionally alkyl substituted carbamoyl or sulphamoyl, or amino (optionally substituted by alkyl, alkoxycarbonyl or alkanoyl) or a group R, RO, RS, RSO or RSO2 in which R represents alkyl (optionally substituted by halogen), and Ar represents a group of the formula: STR2 wherein R4 and R6 each represents halogen or a group R, RO, RS, RSO or RSO2, and R5, R7 and R8 each represents a substituent as defined for R4 and R6, or represents hydrogen, hydroxy, carboxy, nitro, cyano, amino, alkylamino (optionally substituted by alkyl, alkoxycarbonyl or alkanoyl), alkoxycarbonyl or alkanoyl or a pesticidally acceptable salt thereof, with the exclusion of compounds in which R2 and R3 simultaneously represent hydrogen atoms, compositions for use in the method and novel compounds of formula I.
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