Optimization of the macrolactonization reaction conditions^a.

Entry	Base	Yieldb (%)	drc	eed (%)
1	DMAP (1.0 equiv.)	47	92 : 8	99
2	DIPEA (1.0 equiv.)	Trace	—	—
3	Cs2CO3 (1.0 equiv.)	55	92 : 8	99
4	Cs2CO3 (2.0 equiv.)	67	92 : 8	99
5	Cs2CO3 (3.0 equiv.)	58	92 : 8	99
6	Cs2CO3 (1.5 equiv.)	70	93 : 7	99
	DIPEA (0.5 equiv.)

^aAll reactions were carried out with 1a (0.1 mmol), 2a (0.1 mmol), and Sc(OTf)₃/L₃-PiPr₂ (1 : 1, 5 mol%) in DCM (1.0 mL) at 35 °C for 4 h, and then base was added, and the resulting reaction mixture was stirred at 35 °C for 12 h.

^bYield of isolated product 4aa.

^cDetermined by ¹H NMR analysis.

^dDetermined by UPC² analysis on a chiral stationary phase. DMAP = 4-dimethylaminopyridine, DIPEA = N,N-diisopropylethylamine.