THE PREPARATION OF C-ARYL GLUCALS VIA PALLADIUM-CATALYZED CROSS-COUPLING METHODS

The C-aryl glucals 17-31 have been prepared by the palladium-catalyzed cross coupling of 1-tributylstannyl-3,4,6-tri-O-(tert-butyldimethylsilyl)-D-glucal (11) and aryl bromides. The major by-product in all of these reactions is the dimer 33, the product of homocoupling of 11. Alternatively, the C-aryl glucals 34-40 can be obtained from the palladium-catalyzed coupling of 1-iodo-3,4,6-tri-O-(triisopropylsilyl)-D-glucal (16) and a variety of metalated aromatics, including ArZnC1, ArB(OH)(2), and ArB(OMe)(2). The advantages of the latter procedure include superior coupling yields under milder reaction conditions and the high yielding preparation of 16 directly from 3,4,6-tri-O-(triisopropylsilyl)-D-glucal (12) by a metalation-iodination sequence.