Table 3.

Scope of alkynes in the [4+2] annulation.

Entry[a]	Substrate	Alkyne	Product	t [h]	Yield[%][b]
1	1a	2b	5a	16	71
2[c]	1a	2c	5b	16	57
3	1j	2b	5c	16	72
4	1f	2d	5d	14	42
5	1a	2e	5e	12	66
6		2f	5f	14	61
7	1h	2g	5g	24	42
8	1c	2h	5h	12	92

^[a]Reaction condition: substrate (0.2 mmol, 0.1 M in degassed MeOH), 2b–2h (0.6 mmol), 4a (2 mol%), irradiation with two 18 W LED light bulbs.

^[b]Yield of the isolated product.

^[c]Mixed solvent of MeOH and CH₃NO₂ (1:1).