New L-Serine Derivative Ligands as Cocatalysts for Diels-Alder Reaction

Table 2

Results of the Diels-alder reaction between 1 and 2, yield, endo/exo ratio of adduct 3, and enantiomeric excess (e.e.).

Entry	Catalyst	Ligand	Reaction time/h	𝜂/%	Endo/exo ratio^2	e.e./%^3
1	AlCl3	8	4	traces	—	—
2	FeCl3	8	4	<5	—	—
3	Cu(OTf)2^1	8	20	—	—	—
4	Cu(OTf)2^1	4	20	<5	—	—
5	Cu(OTf)2^1	9	20	31	90/10	<1
6	Cu(OTf)2^1	5	20	59	82/18	<1
7	ZnI2	5	4	23	87/13	<1
8	ZnI2^1	5	20	58	87/13	<1
9	Cu(OTf)2^1	6	20	21	86/14	12 (R)
10	ZnI2^1	6	20	30	83/17	24 (R)
11	Cu(OTf)2^1	7	20	57	82/18	8 (R)
12	ZnI2^1	7	20	56	88/12	10 (R)
13	Cu(OTf)2^4	7	20	51	83/17	8 (R)

The reactions were performed with 10% of both catalyst and ligand, at 0°C in dichloromethane, except in the mentioned cases. 10°C to room temp.; 2measured by ¹H-NMR; 3measured by chiral gaseous chromatography. The absolute configuration was determined by comparison with the [𝛼]_𝐷 value of an authentic sample; [15] 410% of catalyst and 20% of ligand.