Copper‐Catalyzed β‐Boration of α,β‐Unsaturated Carbonyl Compounds: Rate Acceleration by Alcohol Additives.

Abstract

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First-Row d-Block Element-Catalyzed Carbon–Boron Bond Formation and Related Processes

“…Density functional theory studies by Lin, Marder and co-workers have shed light on various mechanisms, such as reduction of CO 2 to CO, 164,522 carboxylation of arylboronate esters, 523 diboration of aldehydes, 524 and borylation of α,β-unsaturated carbonyl compounds. 162 Copper complexes with an equally diverse number of ligand sets have been described, most notably phosphino-copper-boryl complexes 525,526 and more recently NHC-based complexes. 163,527 The most recent review dedicated to NHC-based copper-boryl complexes suggests that this class of complexes are the optimal catalysts for enantioselective transformations with these reagents.…”

ChemInform Abstract: Potassium Trifluoroborate Salts as Convenient, Stable Reagents for Difficult Alkyl Transfers

“…However, prior to the work Molander and coworkers performed in this area, there was no precedent of zinc, tin, or boro homoenolates having been employed in cross-coupling reactions with aryl electrophiles. Initial investigations in this area dealt with the preparation of potassium 3-oxoalkyltrifluoroborates via conjugate addition of bis(pinacolato)diboron to unsaturated carbonyl compounds [xlvii] or by alkylation of commercially available methyl ketones (via lithium enolates) with iodomethylpinacol boronate [xlviii] followed in both cases by treatment with KHF 2 . Conditions were then identified allowing cross-coupling of the 3-oxoalkyltrifluoroborates with a variety of aryl bromides.…”

Evolution of a Strategy for the Enantioselective Synthesis of (−)-Cajanusine

“…19 Copper-catalyzed conjugate addition of Bpin and subsequent oxidation resulted in the formation of dione 23 (1:2:1 mixture of keto and enol tautomers). 20 Direct installation of the prenyl group proved challenging, as has been noted in the syntheses of other prenylated natural products. 21 Therefore, an approach involving allylation followed by cross-metathesis with isobutene was explored.…”

“…11 Other approaches involving cuprates proved less fruitful and resulted in the formation of several unidentified impurities. We elected to explore incorporation of the aryl group by cross-coupling of a redox-active ester (20,27), which could be prepared from 19 by oxidation to the acid and coupling with the necessary reagent. As has been noted, cross-coupling reactions of redox-active esters are substrate dependent, and it is therefore difficult to predict the success of any given set of conditions.…”