Synthesis of Boronic Acids and their Esters

Several methods are available for the synthesis of boronic acids and their esters (see also refs. 1-8, 5.3.2.4). Trialkoxyboranes react with polar organometallics. Organo-magnesium halides and organolithiums are most often used. 

Synthesis of Boronic Acids and their Esters 35 1.3.1.3 Coupling of Aryl Halides with Diboronyl Reagents... 

Synthesis of Boronic Acids and their Esters 151 Bpin... 

The synthesis of alkyl-, aryl-, and 1-alkenylboronic acids or their esters from Grignard or lithium reagents and trialkylborates is a classical and efficient method for making relatively simple boron compounds in large quantities (Scheme 2-6) [25]. The stereocontrolled synthesis of alkenylboronic acids and esters involves the reaction of a (Z)- or ( )-2-buten-2-ylmagnesium bromide with trimethyl borate [26]. 

The reaction of 2-bromo-6-lithiopyridine (13) with trialkylboranes gives intermediate boron compounds which are versatile intermediates for the preparation of unsaturated nitriles (Scheme 9). A stereospecific synthesis of dehydronerol utilizes the dianion of 3-methylbut-2-enoic acid as an isoprene functionality (Scheme 10). Lithium dianions from aj8-unsaturated acids generally undergo alkylation reactions at the a-carbon atom. In contrast the dicopper dianions undergo more selective y-alkylation (62—99%) and this ratio is generally higher than with the corresponding esters. A study of various acids and their alkylation with allyl electrophiles showed that allylic electrophiles unsubstituted at the y-carbon react... 

The product 104 is a convenient starting compound for the subsequent modification of photochromes. In particular, publication [116] described an efQcient route for the synthesis of both symmetrical (105) and unsymmetrical (106) phenyl-substimted dihetarylethenes bearing amino, hydroxyl, or carboxyl groups from this dichloride and commercially available substituted boronic acids (or their pinacol esters) via the Suzuki reaction in a DME-H2O (4 1) mixture under reflux (24 h). The yields attain 85-95 % for the symmetrical products and 60 % for the unsymmetrical products. It should be noted however, the McMurry reaction mainly found application in the synthesis of the perhydrocyclopentene analogs of dithienylperfluorocyclopentenes [117]. 

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