Table 1. Optimization of the Intermolecular Lactonization of Styrene 1a with Malonate (2a)^a.

entry	base	solvent	3 (%)	dr (cis:trans)b
1	Ca(OH)2	tBuOH	83	79:21
2	Mg(OH)2	tBuOH	trace
3	Ba(OH)2	tBuOH	74	67:33
4	Sr(OH)2	tBuOH	33	50:50
5	BaCO3	tBuOH	trace
6	SrCO3	tBuOH	trace
7	NaHCO3	tBuOH	32	50:50
8	Na2CO3	tBuOH	77	45:55
9	K2CO3	tBuOH	53	40:60
10	Cs2CO3	tBuOH	49	37:63
11	KOH	tBuOH	36	33:67
12	K3PO4	tBuOH	26	30:70
13	Na2CO3	tBuOH/H2O (2 mL/1 mL)	69	25:75
14	Ca(OH)2	tBuOH/H2O (2 mL/1 mL)	61	40:60
15	Ba(OH)2	tBuOH/H2O (2 mL/1 mL)	7	29:71
16	Sr(OH)2	tBuOH/H2O (2 mL/1 mL)	29	42:58
17	K2CO3	tBuOH/H2O (2 mL/1 mL)	60	26:74
18	Cs2CO3	tBuOH/H2O (2 mL/1 mL)	56	28:72
19	KOH	tBuOH/H2O (2 mL/1 mL)	trace
20	K3PO4	tBuOH/H2O (2 mL/1 mL)	41	27:73

^aReaction conditions: 1a (2 equiv), 2a (0.3 mmol), I₂ (0.3 mmol), and base (0.3 mmol) in solvent (3 mL) were stirred at ambient temperature irradiated with four of compact fluorescent lamps (CFLs) for 20 h.

^bDiasteromeric ratios (dr) were determined by ¹H NMR analysis of the crude reaction mixture.