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. Author manuscript; available in PMC: 2015 Jul 21.
Published in final edited form as: Angew Chem Int Ed Engl. 2014 Jun 10;53(30):7832–7837. doi: 10.1002/anie.201404437

Table 2.

Conditions Favoring Unique Cationic Cyclization Products.

graphic file with name nihms608049u2.jpg
Entry Acid Conditions Adduct Yield (%)[a]
1[b] formic acid Neat
10 °C to rt, 72 h		 graphic file with name nihms608049t1.jpg
(+/−)-7 		30
2 p-TsOH (10 equiv)
LiOTf (10 equiv)		 HFIP (0.015 M)
50 °C, 12 h		 graphic file with name nihms608049t2.jpg
13 		89
3 TFA (0.14 M) Neat
r.t., 24 h		 97
4 p-TsOH (10 equiv)
LiBr (10 equiv)		 CH3NO2 (0.015 M)
r.t., 10 min		 55
5 p-TsOH (10 equiv)
LiBr (10 equiv)		 CH2Cl2 (0.015 M)
−40 °C, 30 h		 graphic file with name nihms608049t3.jpg
14 		55[c]
6 p-TsOH (10 equiv)
LiBr (10 equiv)		 CH3CN (0.015 M)
60 °C, 10 min		 graphic file with name nihms608049t4.jpg
15 		35
7 p-TsOH (10 equiv)
LiBr (10 equiv)		 CH2Cl2 (0.015 M)
−25 °C, 30 h		 graphic file with name nihms608049t5.jpg
16 		97[d]
[a]

Isolated yield of product after silica gel chromatography.

[b]

Product 13 also produced in 34 % yield.

[c]

Product isolated as a mixture of cis and trans isomers.

[d]

Product obtained pure (1H NMR) without need for further purification.