Table 2.

^a

S. no	saltb	Brønsted acid promoter	solvent	T (°C)	total yield (%) (C2 yield)d	dre
1	NaOAc	AcOH	AcOH	RT	50 (6)	1:1
2	NaOAc	AcOH	AcOH/MeOH (9:1)	RT	47 (11)
3	LiOAc	AcOH	AcOH	RT	76 (9)	1:1
4	CsOAc	AcOH	AcOH	RT	55 (6)	1:1
5	KOAc	AcOH	AcOH	RT	55 (6)	1:1
6	AgOAc	AcOH	AcOH	RT	25 (nd)	nd
7	AgOAc	AcOH	AcOH	RT	Decomp.
8c	LiOAc	(R)-BINOL	AcOH	RT	70 (8)	1:1
9c	LiOAc	(S)-BINOL	AcOH	RT	70 (8)	1:1
10c	LiOAc	(R)-BINOL phosphoric acid	AcOH	RT	65 (8)	1:1
11c	LiOAc	(S)-BINOL phosphoric acid	AcOH	RT	65 (8)	1:1

^aReaction conditions: l-Trp-methyl ester (l-Trp-OMe) (220 mg, 0.916 mmol, 1.0 equiv), prenyl bromide (10) (212 μL, 1.83 mmol, 2.0 equiv) in acetic acid (0.1 M), 12 h.

^b2.0 equiv of salt added.

^c1.0 equiv of the Brønsted acid promoter added.

^dIsolated yield after purification by column chromatography and calculated based on recovered starting material: C3/C2-prenylation determined by NMR analyses.

^edr-diastereomeric ratio between exo and endo isomers (by NMR). RT: room temperature; Decomp: substrates decomposed into unverifiable mixture; nd-not determined. Method is scaled up to 0.5 g of l-Trp-OMe, and no reduction in the isolated yield was observed.