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

Table 1

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

Entry	Catalyst	Reaction time/h	𝜂/%	Endo/Exo ratio^c
1	—	4	—	—
2	AlCl3		87	95/5
3	AlMe3		70	93/7
4	FeCl3		75	95/5
5	TiCl4		80	94/6
6	SnCl4		67	94/6
7	Cu(OTf)2		35	98/2
8	ZnI2		11	94/6
9	Cu(OTf)2^a	20	38	85/15
10	ZnI2^a		16	92/8
11	Cu(OTf)2^b	2	32	94/6
12	AlCl3	20	53	91/9

The reactions were performed with 10% of catalyst, at 0°C in dichloromethane, except in the mentioned cases. a0°C to room temp.; b30 % of catalyst; cmeasured by ¹H-NMR.