Table 1.

Lewis Acid Promoted Intermolecular Diels-Alder

Entry	Lewis acid	temp, time	11:12:8[a]	yield (11)[b]
1	TMSOTf	−78 °C, 2 h	1:0:1	18%
2	TiCl4	−20 °C, 0.5 h	1:3:1	24%
3	Ti(iOPr)4	0 °C, 12 h	0:0:1	–
4	Et2AlCl	0 °C, 12 h	0:0:1	–
5	(CH3)3Al	0 °C, 12 h	0:0:1	–
6	EtAlCl2	−20 °C, 1 h	3:1:0	36%
7	EtAlCl2[c]	−78 → −20 °C, 3 h	13:1:1	59%

^[a]Determined by analysis of the crude reaction mixture by ¹H NMR.

^[b]Isolated yield.

^[c]Substitution of CH₂Cl₂ for toluene as the solvent provided 11 in 54% yield.