Palladium-catalyzed oxidative borylation of conjugated enynones through carbene migratory insertion: synthesis of furyl-substituted alkenylboronates

Abstract

A new method for the synthesis of furyl-substituted alkenylboronates has been developed by palladium-catalyzed oxidative borylation reaction of conjugated enynones.

Regioselective trans-Carboboration of Propargyl Alcohols

“…The alkenyl boronate products thus formed lend themselves to numerous downstream transformations; 18 only a few possibilities are shown in Scheme 4: (i) Although proto-deborylation of 10 “wastes” the valuable C–B bond, it leads to the important polyketide motif D cited in the introduction; as shown for product 14 , the reaction can be readily achieved using catalytic AgNO 3 . 19 (ii) Addition of aq NaOH “arms” the remaining boron atom in 10 for cross-coupling with a second electrophilic partner. In this manner, two different hydrocarbyl residues can be stitched trans to each other across the triple bond; 20 the resulting tetrasubstituted alkenes such as 15 are difficult to make in rigorously stereodefined format by other means.…”

Regio‐ and Stereoselective 1,2‐Carboboration of Ynamides with Aryldichloroboranes

“…The triaryl substituted enamide 7 was obtained by Suzuki–Miyaura cross‐coupling of 3 a with 4‐MeC 6 H 4 I in 80 % yield (Scheme 4 c). [17] AgNO 3 ‐catalyzed protodeboration of 5 l gave stereospecifically the disubstituted enamide 8 (87 %) [18] . Treatment of 5 l with NaBO 3 provided the ketone 9 in a good yield and 5 l was successfully converted into the fully substituted cyclopropylboronate 10 using ZnEt 2 /CH 2 I 2 (82 %) [19] …”

“…[17] AgNO 3 -catalyzed protodeboration of 5 l gave stereospecifically the disubstituted enamide 8 (87 %). [18] Treatment of 5 l with NaBO 3 provided the ketone 9 in a good yield and 5 l was successfully converted into the fully substituted cyclopropylboronate 10 using ZnEt 2 /CH 2 I 2 (82 %). [19] Recently, boron-doped polycyclic aromatic hydrocarbons (B-PAHs) have attracted increasing attention because of their interesting materials properties.…”

Synthesis of Alkenylboronates from N-Tosylhydrazones through Palladium-Catalyzed Carbene Migratory Insertion

“…We expected that the boron–palladium species could participate in carbene migratory insertion followed by β-H elimination, which may provide a new approach for the synthesis of alkenylboronates (Scheme ). Herein, we reported our detailed study on the palladium-catalyzed oxidative cross-coupling reaction between N -tosylhydrazones and diboron compounds. This reaction provides an efficient method for diverse synthesis of di-, tri-, and tetrasubstituted alkenylboronates from easily available ketones. − Computational studies substantiate the reaction pathway involving palladium carbene formation and migratory insertion of the boron group.…”