959685-46-2Relevant academic research and scientific papers
Synthesis of α-Chiral Ketones and Chiral Alkanes Using Radical Polar Crossover Reactions of Vinyl Boron Ate Complexes
Gerleve, Carolin,Kischkewitz, Marvin,Studer, Armido
supporting information, p. 2441 - 2444 (2018/01/27)
Vinyl boron ate complexes of enantioenriched secondary alkyl pinacolboronic esters undergo stereospecific radical-induced 1,2-migration in radical polar crossover reactions. In this three-component process various commercially available alkyl iodides act as radical precursors and light is used for chain initiation. Subsequent oxidation and protodeborylation leads to valuable α-chiral ketones and chiral alkanes, respectively, with excellent enantiopurity.
Investigation of the Deprotonative Generation and Borylation of Diamine-Ligated α-Lithiated Carbamates and Benzoates by in Situ IR spectroscopy
Mykura, Rory C.,Veth, Simon,Varela, Ana,Dewis, Lydia,Farndon, Joshua J.,Myers, Eddie L.,Aggarwal, Varinder K.
supporting information, p. 14677 - 14686 (2018/11/20)
Diamine-mediated α-deprotonation of O-alkyl carbamates or benzoates with alkyllithium reagents, trapping of the carbanion with organoboron compounds, and 1,2-metalate rearrangement of the resulting boronate complex are the primary steps by which organoboron compounds can be stereoselectively homologated. Although the final step can be easily monitored by 11B NMR spectroscopy, the first two steps, which are typically carried out at cryogenic temperatures, are less well understood owing to the requirement for specialized analytical techniques. Investigation of these steps by in situ IR spectroscopy has provided invaluable data for optimizing the homologation reactions of organoboron compounds. Although the deprotonation of benzoates in noncoordinating solvents is faster than that in ethereal solvents, the deprotonation of carbamates shows the opposite trend, a difference that has its origin in the propensity of carbamates to form inactive parasitic complexes with the diamine-ligated alkyllithium reagent. Borylation of bulky diamine-ligated lithiated species in toluene is extremely slow, owing to the requirement for initial complexation of the oxygen atoms of the diol ligand on boron with the lithium ion prior to boron-lithium exchange. However, ethereal solvent, or very small amounts of THF, facilitate precomplexation through initial displacement of the bulky diamines coordinated to the lithium ion. Comparison of the carbonyl stretching frequencies of boronates derived from pinacol boronic esters with those derived from trialkylboranes suggests that the displaced lithium ion is residing on the pinacol oxygen atoms and the benzoate/carbamate carbonyl group, respectively, explaining, at least in part, the faster 1,2-metalate rearrangements of boronates derived from the trialkylboranes.
Use of alkyl 2,4,6-triisopropylbenzoates in the asymmetric homologation of challenging boronic esters
Larouche-Gauthier, Robin,Fletcher, Catherine J.,Couto, Irantzu,Aggarwal, Varinder K.
supporting information; experimental part, p. 12592 - 12594 (2012/01/05)
(-)-Sparteine induced lithiation of primary 2,4,6-triisopropylbenzoates and subsequent homologation of boronic esters is reported. A comparative study with lithiated N,N-diisopropylcarbamates has demonstrated the superiority of the hindered benzoate. The Royal Society of Chemistry 2011.
Improved method for the conversion of pinacolboronic esters into trifluoroborate salts: facile synthesis of chiral secondary and tertiary trifluoroborates
Bagutski, Viktor,Ros, Abel,Aggarwal, Varinder K.
supporting information; experimental part, p. 9956 - 9960 (2010/02/27)
A general method for the preparation of virtually any potassium trifluoroborate salt from the corresponding pinacolboronic ester is reported. Thus, conditions for an azeotropic removal of pinacol from the reaction mixture were found to afford the desired potassium trifluoroborates of sufficient purity (>95%) in nearly quantitative yields irrespective of the nature of the product. The utility of this method is illustrated by the preparation of a broad range of enantioenriched secondary and tertiary potassium trifluoroborates.
Lithiated carbamates: Chiral carbenoids for iterative homologation of boranes and boronic esters
Stymiest, Jake L.,Dutheuil, Guillaume,Mahmood, Adeem,Aggarwal, Varinder K.
, p. 7491 - 7494 (2008/09/17)
(Chemical Equation Presented) Take your pick: Either enantiomer of either diastereomer of substrates bearing adjacent stereogenic centers is accessible through reaction of an (R)- or (S)-lithiated carbamate with an (R)- or (S)-boronic ester (see scheme; pin = pinacolate, OCb = substituted carbamate).
