Noncryogenic Preparation of Functionalized Arylboronic Esters through a Magnesium−Iodine Exchange with in Situ Quench

Abstract

Various functionalized aryl boronic esters derived from hexylene glycol and pinacol were prepared in excellent yields according to a simple, safe procedure. The metal-halogen exchange reaction between i PrMgCl 3 LiCl and aryl iodides is performed at 0 °C in the presence of a cyclic borate ester (MPBO i Pr or PinBO i Pr); the organomagnesium intermediate is immediately trapped in situ so that no accumulation of hazardous reactive species can occur. The reaction is very selective, and particularly clean crude products are obtained. The scope of the procedure and the tuning of reaction parameters are investigated.

2,4‐Bis(fluoroalkyl)quinoline‐3‐carboxylates as Tools for the Development of Potential Agrochemical Ingredients

“…Last but not least, we used the iodo derivative 9aA to access the corresponding pinacolboronic ester. Thus, 9aA underwent halogen-metal exchange using iPrMgCl·LiCl, and in-situ trapping with isopropoxypinacolborane following the procedure of Chavant et al [17] 2,4-Bis(difluoromethyl)-3-(pinacolboranyl)quinoline (12aA) was obtained in 54 % yield, along with the hydrolysed compound 13aA, which we have already described, [6] as the sole remnant of the starting material (Scheme 10). Thus, using model substrate 5aA, we have accessed several key 2,4-bis(fluoroalkyl)quinoline building blocks, bearing diverse synthetically useful functional groups at the C-3 position.…”

Recent progress in the synthesis of pyridinylboronic acids and esters

“…Trimethyl borate B(OMe) 3 (4a, R = R 1 = Me), 8 triisopropyl borate B(Oi-Pr) 3 (4b, R = R 1 = i Pr), 8 tributyl borate B(OBu) 3 (4c, R = R 1 = n-Bu) 8,12 and tris(trimethylsilyl) borate B(OSiMe 3 ) 3 (4d, R = R 1 = SiMe 3 ) 13 are the most commonly used starting non-cyclic trialkylborates, while the most commonly used cyclic borates are MeO-Bpin (4e), 14 i PrO-Bpin (4f), 15 and MPB-O i Pr (4g). 16 Under some circumstances, 5 was obtained as a stable intermediate and used directly for Suzuki coupling, 17 but it was generally transformed into a stable pyridinylboronic acid or ester via path A, B, or C prior to use in the coupling reaction. For example, most 3-pyridinylboronic acids and 4-pyridinylboronic acids are stable and can be obtained by quenching the reaction mixture with aqueous acid or base (path A in Scheme 1, via 4a-d, R = R 1 ).…”

“…5,6,13,17,[34][35][36][37][38][39][40][41][42] In the particular case of compound 3 (X = 2-I), 2-iodopyridine was used. 16 To improve the stability (particularly in air and water), pyridine-2-boronates such as 6, 34 7, 35,36 and 8 37,38 were developed. e The yields refer to the corresponding product 1A and 1B(Pin).…”

Überwindung der Limitierungen für die Lithiierung von Organoborverbindungen durch kontinuierliche Prozessführung

“…[4,5] Jedoch werden diese Methoden in der Industrie eher selten oder überhaupt nicht genutzt, hauptsächlich da sie teure und exotische Katalysatoren, Liganden und Bor-Quellen erfordern. Die kostengünstigsten und überwiegend genutzten Verfahren für die industrielle Herstellung von Organoborverbindungen sind daher immer noch die diskontinuierlichen Reaktionen eines Organolithium- [4,6] oder Organomagnesiumintermediats [4,7] [12] Der Prozess umfasst einen Halogen-Lithium-Austausch, eine Borylierung und eine SuzukiMiyaura-Kreuzkupplung. Das Problem der Reaktorblockierung durch das Ausfällen von Feststoffen wurde durch Ultraschallbehandlung umgangen, was zugleich ein gutes Durchmischen für die Drei-Phasen-Suzuki-Miyaura-Kreuzkupplung garantierte.…”