Preparations of Hexyleneglycol Arylboronic Esters

2 In situ Iodine-Magnesium Exchange and Trapping of Sensitive Arylmagnesium Reagents 

The main advantage of this procedure is that all organomagnesium species are immediately consumed, which suppresses the aforementioned stability issues. Excellent conversions and very good isolated yields are obtained. The process does not apply to aryl bromides. It should be emphasized that this method is particularly suited for electron-deficient aryl iodides and thus complements other borylation pathways, which are generally less efficient when applied to such aryl halides. Note that such a procedure is also efficient for lithium-halide exchange, although low temperatures are required.  

Rhodium- and Ir-catalyzed C-H borylation of arenes are nowadays important pathways. The regioselectivity of the first successful reactions were chiefly under steric control (to the least hindered positions), often offering a simple access to positions (for instance position 5 of 1,3-dimethoxy-benzene) where installation of a halide group for Pd-catalyzed borylation is difficult. These successes prompted a promising development of strategies for directed C-H borylations.  

Thus the catalyzed borylation of aryl iodides, bromides, chlorides or sulfonates with HBhg proceeds readily, in excellent yields and chemoselectivi-ties. The products are perfectly stable to air, water and chromatography. It can thus be considered as a good, inexpensive alternative to the analogous Pd-catalyzed borylation with HBpin, particularly when the substrates are sulfonates or electron-rich halides. 

So it is, nowadays, clear that replacement of the expensive and somewhat limiting (Section 3.5.2.2) pinacol by other diols in the preparation of stable 

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