A process for the synthesis of oligonucleotides using phosphoramidite
chemistry is provided. The process employs as activator a
1,1-dioxo-1,2-dihydro-1.lamda..sup.6-benzo[d]isothiazol-3-one, preferably
in the presence of an organic base. The
1,1-dioxo-1,2-dihydro-1.lamda..sup.6-benzo[d]isothiazol-3-one is
represented by the following structural formula: ##STR00001## wherein p
is 0 or an integer from 1 to 4; X.sup.7 is O or S; R for each occurrence
is a substituent, preferably each independently, a halo, a substituted or
unsubstituted aliphatic group, --NR.sup.11R.sup.12, --OR.sup.13,
--OC(O)R.sup.13, --C(O)OR.sup.13, or cyano; or two adjacent R groups
taken together with the carbon atoms to which they are attached form a
six membered saturated or unsaturated ring; R.sup.11 and R.sup.12 are
each, independently, --H, a substituted or unsubstituted aliphatic group,
a substituted or unsubstituted aryl group, or a substituted or
unsubstituted aralkyl group; and R.sup.13 is a substituted or
unsubstituted aliphatic group, a substituted or unsubstituted aryl group,
or a substituted or unsubstituted aralkyl group. Preferred organic bases
are pyridine, 3-methylpyridine, or N-methylimidazole.