Table 1.

Enantiomeric excesses of Diels–Alder products using different copper catalyst assemblies^[a]

Ligand		a	b	c	d	e
	–	2	13	32	31 (90:10)[b]	72 (90:10)[b]
CB [6]	0	2	–	–	–	–
CB [7]	1	–	9	10	13	55
CB [8]	0	–	12	32	73 (96:4)[b]	92 (97:3)[b]

[a] General conditions: 1 a (1.5 μmol), 2 (4 μL), Cu²⁺ (3 % mol), a–e (4.5 % mol), CB[n] (6 % mol) in 1 mm phosphate buffer (PBS) with pH 7.4, for 24 h at 6 °C. Data were obtained from the crude product on chiral phase HPLC. The ee values are averaged over two experiments and are reproducible within ±2 %. [b] Endo/exo ratios are in parentheses. In all reactions, conversions determined by HPLC are >99 %. The absolute configuration of the main products were identified as the (2R,3R)-enantiomer.