Cross‐Coupling Reactions of Organotrifluoroborate Salts

Abstract

Organotrifluoroborates are partners for cross‐coupling that have emerged as complementary and often unique alternatives to other organoboron reagents. This chapter provides a comprehensive overview of all cross‐coupling reactions of the various classes of organotrifluoroborates that have been carried out through August, 2009. The chapter introduces the subject with a discussion of mechanistic considerations concerning the cross‐coupling, followed by a brief discussion of the stereochemical aspects of the transformation. The scope and limitations of the reactions are subsequently discussed, first in terms of the organotrifluoroborate and then the electrophilic partner of the reaction. Potential side reactions that are encountered are outlined with useful suggestions on how these can be avoided in practice. Applications in synthesis are described, detailing how organotrifluoroborates have been utilized in the construction of natural products, materials of all types, and pharmacologically active substances. A comparison to other cross‐coupling methods rounds out the descriptive part of the chapter. A detailed outline of experimental considerations and protocols has been assembled, gleaning information from the vast array of published procedures to assemble an overview of the most successful conditions. Representative procedures are included for each class of organotrifluoroborate coupling partner, and the tables provide a comprehensive listing of individual reactions.

Organotrifluoroborates: Another Branch of the Mighty Oak

“…28 As an air-and moisture-stable solid that can be stored for months with no special precautions, this material serves as an excellent vinylating agent in cross-coupling reactions with aryl and heteroaryl iodides, bromides, chlorides, diazonium salts, and triflates. 21 The Journal of Organic Chemistry Perspective More highly elaborated alkenyltrifluoroborates of all kinds have been used in coupling reactions with both aryl and heteroaryl electrophiles (eqs 16 and 17). 29 Numerous functional groups have been embedded within the alkenyltrifluoroborates, including halides, ketones, and esters, and the reactions are stereospecific with regard to the olefin geometry of the alkenyltrifluoroborate.…”

Improving Transformations Through Organotrifluoroborates

“…Although organotrifluoroborates have proven efficient and often advantageous when compared to even the most generic boronic acid and boronate ester analogues [21], one advantage of these reagents that has been exploited recently is the availability of novel and highly useful organotrifluoroborates whose complements do not exist among other boronic acid derivatives. One such set of example are the halomethyltrifluoroborates, the syntheses of which spawned whole new families of highly valuable building blocks for organic synthesis (Scheme 9) [22].…”

A modified procedure for the palladium catalyzed borylation/Suzuki-Miyaura cross-coupling of aryl and heteroaryl halides utilizing bis-boronic acid

“…9 This decomposition is exacerbated by the high temperatures and strong base sometimes needed in cross-coupling reactions, and therefore a large excess of the heterocyclic boronic acid is usually required for successful transformations. 10 Boronic acids also form dimeric and cyclic trimeric anhydrides, making the amount of material actually used somewhat challenging to assess. For these reasons, the synthesis, storage, and subsequent cross-coupling of more stable, “protected” boron species in the form of boronate esters and trifluoroborates remains an active area of research.…”

“…As demonstrated frequently in the literature, trifluoroborates (RBF 3 K) remain the more atom economical choice for protecting boron coupling partners for storage, and numerous methods have been reported with high-yielding coupling. 10 …”