Table 2.

Coupling of N-Phthalimidoyl Oxalate 3a with Methyl Vinyl Ketone (MVK) Under Various Reaction Conditions^a

Entry	Modification	Yield of 5 (%)b
1	none	82
2	reaction time of 2 h	81
3	no light	<5%
4	no Hantzsch ester	ND
5	no photocatalyst (2 h)	28
6	no photocatalyst (18 h)	67
7	no i-Pr2NEt•HBF4	72
8	oxalate 3a (1 equiv)	67
9	oxalate 3a (1.1 equiv)	68
10	oxalate 3a (1 equiv) MVK (1.5 equiv)	57

^aConditions of eq 2 using i-Pr₂NEt•HBF₄; [3a] = 0.15 M.

^bIsolated yield after silica gel chromatography.

ND = not detected.