The Boron‐Wittig Olefination of Aldehydes and Ketones with Bis[(pinacolato)boryl]methane: an Extended Reaction Scope

Abstract

Preparation of 2,2‐disubstituted and 2‐monosubstituted alkenylboronic acid esters from aliphatic and aromatic ketones and aldehydes by the boron‐Wittig olefination with bis[(pinacolato)boryl]methane was examined and applied on the multigram scale. The influence of the substrate steric and electronic features on the overall efficiency and stereochemical outcome of the reaction was studied. Additionally, a series of diversely functionalized (hetera)cycloalkylidenemethyl and (hetera)cycloalkyl boronic acid‐derived building blocks was synthesized.

Photochemical [2+2] Cycloaddition of Alkynyl Boronates

“…[3+2] cycloaddition of bicyclic adduct 8 c with azomethine yilde precursor 16 resulted in product 17 in 55–61 % yield using either TFA‐ [58] or LiF‐promoted [59] ylide generation. Treatment of either pure or non‐purified boronate 8 c with KHF 2 provided trifluoroborate 8 cl in 87 and 71 % yield (over two steps), respectively [6] . The reaction of the obtained trifluoroborate 8 cl with Langlois reagent [60,61] gave product 18 resulting from cyclobutene ring opening in 20 % yield (along with 14 and its methyl ester as the main by‐products).…”

“…Treatment of either pure or non-purified boronate 8 c with KHF 2 provided trifluoroborate 8 cl in 87 and 71 % yield (over two steps), respectively. [6] The reaction of the obtained trifluoroborate 8 cl with Langlois reagent [60,61] gave product 18 resulting from cyclobutene ring opening in 20 % yield (along with 14 and its methyl ester as the main by-products). At the same time, addition of a freshly prepared dimethyl dioxirane (DMDO) solution [62] to 8 cl resulted in a partially saturated "Dewar furan" analogue 19 [63] containing a tricyclic system of fused three-, four, and five-membered rings (ca.…”

“…After the development of efficient Suzuki‐Miyaura cross‐coupling protocols, compounds bearing $${{C}_{{sp}^{2}}}$$ ‐B bonds (i. e., (het)aryl or akenyl boronates) rapidly become highly desirable targets for synthetic organic chemists. Traditionally, these compounds have been prepared via hydroboration, [2] Miyaura borylation, [3] metalation‐borylation, [4] boron‐Wittig olefination, [5,6] and other methods [7–10] . One of the recent trends in the field of organoboron reagents and the corresponding C−C‐bond‐forming reactions is related to shift from aromatic compounds towards saturated and partially saturated ring systems [11,12] complying with lead‐likeness concepts in drug discovery [13–15] .…”

gem‐Difluorocyclopropanation of Alkenyl Trifluoroborates with the CF3SiMe3–NaI System

“…The following evaluation of the difluorocyclopropanation reaction efficiency with the TMSCF 3 –NaI system was carried out with three types of trifluoroborate substrates – acyclic, exocyclic and endocyclic alkenes 7 . For our study, trifluoroborates 7a – d and 7m were accessed from commercial sources, whereas substrares 7e – k and 7n , o were obtained from the corresponding pinacolboronates 9 by treatment with KHF 2 in MeOH (Scheme ). Of them, compounds 9f – l and 9n were prepared according to the previously reported procedures , ,…”

Chan–Evans–Lam N1-(het)arylation and N1-alkеnylation of 4-fluoroalkylpyrimidin-2(1H)-ones

“…In view of the availability of boronic acid pinacol esters, and particularly of synthetically attractive pinacol alkenylboronates [ 53 – 54 ], we studied the reaction of 1а with a series of such reagents 6b – d and 7a – h ( Scheme 2 ). The yields of (het)aryl-substituted products 3g , q , s obtained from 6b – d were found to be much the same as in the analogous reactions of substrate 1а with the corresponding boronic acids 2g , q , s .…”