Table 1.

Epoxidation of Ketene Dimers Leading to 1,4-Dioxaspiro[2.3]hexan-5-ones 194/196

entry	R	cmpd.	dr (194:196)b	% yieldc
1	n-Bu	194a	14:1	80
2	CyCH2	194b	10:1	76
3	PhCH2	194c	24:1	57
4	(i-Pr3)SiO(CH2)4	194d	17:1	40
5	N3(CH2)4	194e	16:1	61

^aEpoxidations were performed at ~0.1M concentration using isolated, purified ketene dimers 195a–e prepared by the method of Calter.⁹⁵

^bRatios determined by analysis of crude reaction mixtures by ¹H NMR (500 MHz).

^cRefers to isolated, purified (SiO₂) yields.