Table 4.

Scope of the Diels-Alder-reaction.

entrya	1 [R1, R2]	R3	conditionb	3	yield [%]c	ee [%]d
1	1a [H, H,]	Ph (2a)	A	3a	96	36
2	1b [H, Cl]	2a	A	3b	95	41
3	1a	iPr (2b)	B	3c	74	26
4	1a	t-Bu (2c)	B	3d	45	30
5	1a	Cy (2d)	B	3e	83	42
6	1c [Cl, H]	2d	B	3f	90	19
7	1a	Bn (2e)	A	3g	95	20
8	1a	CHPh2 (2f)	A	3h	85	26
9	1a	4-Br-(C6H4)- (2g)	B	3i	70	13
10	1a	4-MeO-(C6H4)- (2h)	A	3j	82	32
11	1a	2,6-iPr2-(C6H3)- (2i)	B	3k	13	76
12	1a	2i	C	3k	65	51
13	1c	2i	C	3l	77	34
14	1b	2i	C	3m	76	54 (96)e

^aAll reactions were carried out using 0.1 mmol maleimide, 1.1 equiv anthrone in 1 mL abs. CH₂Cl₂. ^bA = 10 mol% 8c, −40 °C, 48 h; B = 25 mol% 8a, −70 °C, 96 h; C = 25 mol% 8a, r.t., 3 h. ^cIsolated yield after column chromatography. ^dThe enantiomeric excess was determined by HPLC using a Chiralpak IA column. ^eRecrystallized from 2-propanol/n-hexane.