Table 1.

Additive screening for ring-closing metathesis of 1 catalyzed by soluble Hoveyda–Grubbs second-generation catalyst ¹.

Entry	Additives	Conversion 2 (%)	Relative Activity (%) 3
1	-	80 2	100
3	BF3-Et2O	60	75
4	TMSOTf	50	62
5	Pyridine	32	40
6	Adenosine	44	55
7	1-butyl-3-methylimidazolium tetrafluoroborate	87	109
8	1-ethyl-3-methylimidazolium methyl sulphate	88	110
9	1-ethyl-3-methylimidazolium tetrafluoroborate	87	109
10	PEG400	90	112
11	PEG600	76	95
12	PEG6000	85	106
13	phenyl-boronic acid	100	125
14	dl–Asp–(OMe)–OMe	25	31
15	NHAc–Cys–Phe–Phe–CONH2	85	106
16	NHAc–Asp–Gly–Asp–Cys–Asp–CONH2	69	86
17	Modified with BOC–Ala–Gly–COOH	15	19

¹ Reaction conditions: 1 (8 µL, 0.033 mmoles), tetrahydrofuran (THF) (1 mL), catalyst (1 mg), 10 eq additive, 20 min and 25 °C; ² we stopped the standard reaction at 80% conversion in order to see possible improvements in the activity after addition of additives; ³ Relative activity is the percentage calculated considering the results of the reaction without additives as 100%.