An Efficient Benzoxaborole One‐Pot Synthesis by SiliaCatDPP‐Pd Heterogeneous Catalysis using Diboronic Acid

Abstract

Organoboron compounds are valuable molecules of increasing interest in organic synthesis, catalysis, biology and medicine. Among them, benzoxaboroles emerged as promising building blocks for numerous research programs. In this letter, we communicate the development of new conditions for the one‐pot benzoxaborole synthesis by SiliaCat DPP−Pd catalysis using diboronic acid as the boron source. This low cost and sustainable strategy permitted the preparation of a useful range of benzoxaborole building blocks. Finally, the transformation was extended to a continuous flow process using our Vapourtec system.magnified image

Modular Synthesis of Complex Benzoxaboraheterocycles through Chelation-Assisted Rh-Catalyzed [2 + 2 + 2] Cycloaddition

“…Regarding oxaborole ring size (Scheme 3d), 5-( 10), 6-( 19), and 7-membered (18) rings could be accessed in generally good yields; however, the formation of an 8-membered oxaborole (37) was not possible and instead, the aryl BMIDA isolated. Intriguingly, 38 was isolated after the deprotection protocol, implying that the BMIDA cleavage for 10, 18, and 19 was facilitated by the presence of the alcohol, for example, via dissociation of the N-methyl group on the BMIDA and association of the alcohol as shown in proposed intermediate 39.…”

“…Classical approaches to the BOB framework have been based on nucleophilic addition of stoichiometric organometallics to a borylated arene bearing an adjacent carbonyl or borylation of an ortho -halo benzyl alcohol derivative using Miyaura-type conditions (Scheme a). − Contemporary approaches include B-insertion strategies using B–Br reagents (Scheme b), such as a dual Ni/Zn catalysis to insert a boron unit into the C­(sp 3 )–O bond of benzodihydrofurans by Dong and co-workers and the electrophilic haloboration approach reported by Ingleson and co-workers to directly access benzoxaboronines from o -alkynyl phenols . A complementary approach that does not rely upon electrophilic borylating agents or C–B bond formation was developed by Sheppard and co-workers, where gold catalysis generated the benzoxaborinine from o -alkynyl boronic acids …”

Modular synthesis of complex benzoxaboraheterocycles through chelation-assisted Rh-catalyzed [2+2+2]cycloaddition

“…Regarding oxaborole ring size (Scheme 3d), 5-( 10), 6-( 19), and 7-membered (18) rings could be accessed in generally good yield; however, the formation of an 8membered oxaborole (37) was not possible and instead the aryl BMIDA 38 was isolated. Intriguingly, 38 was isolated after the deprotection protocol, implying the BMIDA cleavage for 10, 18, and 19 was facilitated by the presence of the alcohol, for example, via dissociation of the N-methyl group on the BMIDA and association of the alcohol as shown in proposed intermediate 39.…”

“…Classical approaches to the BOB framework have been based on nucleophilic addition of stoichiometric organometallics to a borylated arene bearing an adjacent carbonyl, 34 or borylation of an ortho-halo benzyl alcohol derivative using Miyaura-type conditions (Scheme 1a). [35][36][37] Con-temporary approaches include B-insertion strategies using B-Br reagents (Scheme 1b), such as a dual Ni/Zn catalysis to insert a boron unit into the C(sp 3 )-O bond of benzodihydrofurans by Dong and coworkers, 38 and the electrophilic haloboration approach reported by Ingleson and coworkers to directly access benzoxaboronines from oalkynyl phenols. 39 A complementary approach that does not rely upon electrophilic borylating agents or C-B bond formation was developed by Sheppard and coworkers, where gold catalysis generated the benzoxaborinine from o-alkynyl boronic acids.…”