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. Author manuscript; available in PMC: 2012 Oct 26.
Published in final edited form as: Tetrahedron Lett. 2011 Oct 26;52(43):5550–5553. doi: 10.1016/j.tetlet.2011.08.071

Table 3. Tryptamine Investigation for Phosphoric Acid-catalyzed Spirocyclization.

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entry product R R1 R2 method chiral acid yield %[a] er[b]
1 4bb Cl 6-OCH3 H A 8b 99 60:40
2 4bb Cl 6-OCH3 H B 8d 39 80:20
3 4bc Cl H H A 8b 93 67:33
4 4bc Cl H H B 8d 89 65:35
5 4cb H H H A 8b 35 95:5
6 4cb H H H B 8d 71 95:5
7 4bd Cl H CO2CH3 A 8b no rxn --
8 4ad Br H CO2CH3 B 8d 21 52:48
9 4ad Br H CO2CH3 A 8e 92 59:41

Method A: 20 mol % catalyst in CH2Cl2 at 23°C for 72-96h.

Method B: 10 mol % catalyst in DMF at 40°C for 24-48h.

[a]

Isolated yield.

[b]

Enantioselectivity determined by chiral phase HPLC.