Table 1:

Summary of reaction optimization.^[a–c]

Entry	Deviation from standard procedure	t [h]	Yield 5 [%]
1	PhMe, 1 equiv DMAP	6	16[d]
2	PhMe	6	0
3	PhMe/THF (2:1)	2	80
4	none	1	94
5	TFA as proton source[e]	1	92
6	none, gram scale	1	89
7	commercial solution of 1[f]	6	70[d]

^[a]Yields are based on isolated 5.

^[b]Reactions were carried out on a 0.2 mmol scale.

^[c]Reagent 1 was prepared directly before use.^[25]

^[d]Reflects conversion of 4 into 5 as judged by ¹H NMR spectroscopic analysis of the unpurified reaction mixture.

^[e]The reaction was treated with TFA at −78°C and warmed to rt.

^[f]Commercial 1 at 0.52 m (in PhMe) was used as received.