Process for the preparation of certain triaryl rhamnose carbamates

A process for preparing a boronic ester of the formula (IIIa)

• wherein
• R, R1 and R2 independently represent C1-C4 alkyl, C3-C4 alkenyl or C1-C4 fluoroalkyl, and
• R3 and R4 independently represent C1-C4 alkyl, or when taken together form an ethylene or propylene group optionally substituted with from one to four CH3 groups,
• which comprises contacting a boronate substituted phenyl isocyanate of Formula (VII)
• wherein
• R3 and R4 independently represent C1-C4 alkyl, or when taken together form an ethylene or propylene group optionally substituted with from one to four CH3 groups,
• with a tetrahydropyran-2-ol of Formula (IV)
• wherein
• R, R1 and R2 independently represent C1-C4 alkyl, C3-C4 alkenyl or C1-C4 fluoroalkyl,
• in a polar aprotic solvent in the presence of cesium carbonate.