Table 1. Effect of Temperature, Oxygen, and Scale.

entry	T (°C)	t (h)	yield of 2a	yield of 1a	exo:endo ratioa
1	22	16	57	<5	5.5:1
2	5	8	53	<5	5.1:1
3b	22	16	24	42	4.3:1
4c	5	12.5	6	80	3.3:1
5d	5	12.5	22	44	2.7:1
6e	5	12.5	33	29	4.6:1
7f	5	13	40	26	3.5:1
8g	5	13	40	23	3.3:1

^aCalculated by UPLC (PDA).

^bReaction performed at a 0.50 mmol scale.

^cReaction deoxygenated via freeze–pump–thaw.

^dReaction performed under a balloon of oxygen.

^eReaction performed under a balloon of air.

^fReaction sparged continuously with air (0.25 mmol scale).

^gReaction sparged continuously with air (0.50 mmol scale).