Table 2.

Study on ditosylation reactionof N-Boc-serinol (2).

Entry	Solvents	Reaction time	TsCl : TEA	Yields (%)	Mono/di ratio
1	Py	6 h	2.4 : 3	29	10 : 1
2	Py	10 h	3 : 4	40	10 : 1
3	Py, DMAP cat	6 h	3 : 4	31	10 : 1
4	DCM, Py cat	6 h	2.4 : 3	53	5 : 1
5	DCM, Py cat	10 h	3 : 4	45	5 : 1
6	DCM	6 h	3 : 4	55	1 : 1
7	dry DCM	10 h	3 : 4	68	1 : 2
8	dry DCM	10 h	2.4 : 3	85	1 : 19