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. Author manuscript; available in PMC: 2012 Dec 23.
Published in final edited form as: Tetrahedron. 2011 Dec 23;67(51):9809–9828. doi: 10.1016/j.tet.2011.09.035

Table 1.

Cyclization of (−)-44

graphic file with name nihms327891u2.jpg
Entry Acid Equiv Temp (°C) Time (h) Ratiob 21/45 Conv.b (%)
1 CSA 0.1 25 28 1:1 97
2 BF3•OEt2 0.1 −78 25 1:6 10
3 BF3•OEt2 0.1 0 1 1:1 100
4 BF3•OEt2 0.1 40 0.5 1:1 100
5 BF3•OEt2 1.0 −78 1 1:3 80
6 BF3•OEt2 2.0 0 0.3 1:1 100
a

Entries 1–6 were run in CH2Cl2.

b

Ratios and conversions were determined by 1H NMR.