Table 2.

Lewis acid catalyzed, enantioselective photocycloaddition reactions of phenanthrene‐9‐carboxaldehydes (1) and 2,3‐dimethyl‐2‐butene.

Entry[a]	Substrate	X	Y	Product	Yield[b] [%]	ee [c] [%]
1	1 a	H	H	2 a	79	94
2	1 b	2‐Me	H	2 b	75	84
3	1 c	2‐Cl	H	2 c	89	88
4	1 d	3‐F	H	2 d	78	93
5	1 e	3‐Me	H	2 e	66	92
6	1 f	H	5‐Me	2 f	85	86
7	1 g	H	6‐CF3	2 g	92	92
8	1 h	H	6‐F	2 h	79	82
9	1 i	2‐Me	6‐CF3	2 i	89	90
10	1 j	3‐Me	6‐CF3	2 j	93	92
11	1 k	3‐F	6‐CF3	2 k	85	96

[a] The reaction was performed at −78 °C with a substrate concentration of c=20 mm in CH₂Cl₂ at the indicated wavelength (λ) and for the indicated period of time (t). The olefin was used in excess (30 equiv). [b] Yield of isolated product. [c] The ee was determined by chiral‐phase HPLC analysis.