5 -Methylthio-l//-tetrazole

The use of 5-methylthio- l//-tetrazole as the coupling agent also allows the primary hydroxyl group in unprotected carbohydrates and nucleosides to he selectively phosphitylated (eq 2). When the same reactions are performed with l//-tetrazole as the activator, much worse selectivity is observed, resulting in diminished yields. 

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