Investigations of the pivotal IEDDA reaction (the second step of asymmetric catalysis)^a.

Entry	Conditions	Results	Products
1b	(S)-11 (1.5 equiv.)	78%, 3.1 : 1 dr	anti-9, 94% ee
	Yb(OTf)3		ent-syn-9, 94% ee
2	(rac)-11 (2.0 equiv.)	73%, 1.2 : 1 dr	anti-9, 78% ee
	Yb(OTf)3, (S)-L1, DIPEA		syn-9, 90% ee
3	(R)-11 (1.5 equiv.)	75%, 3.8 : 1 dr	syn-9, >99% ee
	Yb(OTf)3, (S)-L1, DIPEA		ent-anti-9, 72% ee
4	(S)-11 (1.5 equiv.)	87%, 10 : 1 dr (4.34 g)	anti-9, 98% ee
	Yb(OTf)3, (S)-L1, DIPEA		ent-syn-9, 19% ee

^aReaction conditions: 10 (0.10 mmol), 11 (0.15 mmol), Yb(OTf)₃ (10 mol%), (S)-L1 (12 mol%), DIPEA (24 mol%), 4 Å M.S. (25 mg), DCM (0.25 mL) at 25 °C.

^b(S)-L1 was not added. DCM, dichloromethane; DIPEA, N,N-diisopropylethylamine; M.S., molecular sieves.