572875-44-6Relevant articles and documents
Regioselective synthesis of: Ortho -iodobiphenylboronic acid derivatives: A superior catalyst for carboxylic acid activation
Al-Jammal, Walid K.,Al-Zoubi, Raed M.,McDonald, Robert
, p. 3612 - 3623 (2020)
An efficient and versatile synthesis of ortho-iodobiphenylboronic acids via the highly regioselective metal-iodine exchange (MIE) of 2,3-diiodobiphenyls is reported. The site-selectivity is very much controlled by the size of the biphenyl fragment, providing only the terminal arylboronic acid derivatives in excellent site-selectivity. The nature of the substituents (R1 and R2) on the biphenyls is found to have an influence on the reactivity but not on the regioselectivity. The best reactivity and the highest isolated yields were furnished with products bearing electron-donating groups. The synthesized derivatives were also tested for in vitro antimicrobial activity against four strains of bacteria and one fungal strain. This revealed that (2-iodo-4′-isopropyl-[1,1′-biphenyl]-3-yl)boronic acid 6A and (3-(benzo[d][1,3]dioxol-5-yl)-2-iodo-5-methoxyphenyl)boronic acid 22A possess the most potent antibacterial and antifungal activity with MICs of 0.10 and 0.3 mg mL-1 for B. cereus and C. albicans respectively. The catalytic activity was also examined towards an amidation reaction at ambient temperature and this revealed a new optimal catalyst, (2-iodo-4′,5-dimethoxy-[1,1′-biphenyl]-3-yl)boronic acid 19A providing a remarkable increase in the amide yields, including α-aminoacids. This work discloses a protocol for the first synthesis of hitherto unknown ortho-iodobiphenylboronic acid derivatives that is scalable, and general in scope, where no chromatographic purification is necessary and the products are indeed potential organocatalysts.
Solid-supported ortho-iodoarylboronic acid catalyst for direct amidation of carboxylic acids
Gernigon, Nicolas,Zheng, Hongchao,Hall, Dennis G.
supporting information, p. 4475 - 4478 (2013/07/26)
Amides are a ubiquitous class of organic compounds endowed with great utility. There is a need for simple and effective catalytic methods for their direct formation from carboxylic acids and amines as a way to avoid the use of coupling reagents. We have designed a recyclable resin-supported derivative of 5-methoxy-2-iodophenylboronic acid as a heterogeneous catalyst active in ambient conditions for promoting direct amidations of aliphatic carboxylic acids and amines. The optimal, practical procedure involves a simple double-filtration to isolate the amide product while separating the catalyst from residual molecular sieves.
Direct amidation of carboxylic acids catalyzed by ortho-iodo arylboronic acids: Catalyst optimization, scope, and preliminary mechanistic study supporting a peculiar halogen acceleration effect
Gernigon, Nicolas,Al-Zoubi, Raed M.,Hall, Dennis G.
, p. 8386 - 8400 (2013/01/15)
The importance of amides as a component of biomolecules and synthetic products motivates the development of catalytic, direct amidation methods employing free carboxylic acids and amines that circumvent the need for stoichiometric activation or coupling reagents. ortho-Iodophenylboronic acid 4a has recently been shown to catalyze direct amidation reactions at room temperature in the presence of 4A molecular sieves as dehydrating agent. Herein, the arene core of ortho-iodoarylboronic acid catalysts has been optimized with regards to the electronic effects of ring substitution. Contrary to the expectation, it was found that electron-donating substituents are preferable, in particular, an alkoxy substituent positioned para to the iodide. The optimal new catalyst, 5-methoxy-2-iodophenylboronic acid (MIBA, 4f), was demonstrated to be kinetically more active than the parent des-methoxy catalyst 4a, providing higher yields of amide products in shorter reaction times under mild conditions at ambient temperature. Catalyst 4f is recyclable and promotes the formation of amides from aliphatic carboxylic acids and amines, and from heteroaromatic carboxylic acids and other functionalized substrates containing moieties like a free phenol, indole and pyridine. Mechanistic studies demonstrated the essential role of molecular sieves in this complex amidation process. The effect of substrate stoichiometry, concentration, and measurement of the catalyst order led to a possible catalytic cycle based on the presumed formation of an acylborate intermediate. The need for an electronically enriched ortho-iodo substituent in catalyst 4f supports a recent theoretical study (Marcelli, T. Angew. Chem. Int. Ed.2010, 49, 6840-6843) with a purported role for the iodide as a hydrogen-bond acceptor in the orthoaminal transition state.
