. Author manuscript; available in PMC: 2013 Jul 1.

Published in final edited form as: European J Org Chem. 2012 Jun 13;2012(22):4130–4139. doi: 10.1002/ejoc.201200286

Table 1. Reaction optimization for oxidative cyclization of 17^[a].

Entry	Acid	Solvent	Yield
1	InCl₃	CH₂Cl₂	57%
2	InCl₃^[b]	CH₂Cl₂	55%
3	AlCl₃	CH₂Cl₂	N.D.
4	LiClO₄	CH₂Cl₂	41%
5	LiClO₄^[b]	CH₂Cl₂	46%
6	TiCl₄	CH₂Cl₂	N.D.
7	CSA	CH₂Cl₂	65%
8	CSA	CH₃CN	69%
9	PPTS	CH₃CN	71% ^[c]
10	PPTS	CH₃CN	81% ^[d]

^[a]

Reaction conditions: the reaction was carried out on a 0.5 mmol scale, acid (1.5 equiv.), 4 Å MS, for CH₂Cl₂ at −78 °C, for CH₃CN at −38 °C, 6-8 h;

^[b]

with 2,6-dichloropyridine (1.5 equiv.);

^[c]

20 mol-% DDQ and 2 equiv CAN

^[d]

4 grams scale 17. CAN = ceric ammonimum nitrate.

Table 1. Reaction optimization for oxidative cyclization of 17[a].