Screening of cyclization conditions to generate 19^a.

Entry	Reagent	Solvent	Temperature (°C)	19 : 32	Yield (%)
1	BDSB	EtNO2	−78	4.9 : 1	∼30 b.r.s.m.
2	BDSB	MeNO2	−20	5.3 : 1	∼30 b.r.s.m.
3	BDSB	MeNO2	0	1.3 : 1	20%
4	BDSB	CH2Cl2	−20	N/A	<10% conv.
5	BDSB	CH2Cl2	0	7.0 : 1	49%
6	NBS, morpholine	HFIP	0 to reflux	N/A	N.R.

^aReactions were performed using 0.06 mmol of 23; all reactions using BDSB were conducted for 10 min total.