Abstract
Stirring α,β-unsaturated α-diketones in the presence of activated silica gel results in cyclization to α-hydroxycyclopentenones in good yield. The reaction is sensitive to the mode of stirring and proceeds more rapidly in the presence of triethylamine. This is consistent with a Nazarov reaction proceeding through the enol tautomer of the α-diketone.
Key words
diketones - cyclizations - Nazarov reactions - silica gel - rearrangements
References
1 Batson WA.
Sethumadhavan D.
Tius MA.
Org. Lett.
2005,
7:
2771
2a Baldwin JE.
J. Chem. Soc., Chem. Commun.
1976,
734
2b Baldwin JE.
Cutting J.
Dupont W.
Kruse L.
Silberman L.
Thomas RC.
J. Chem. Soc., Chem. Commun.
1976,
736
2c Baldwin JE.
Kruse LI.
J. Chem. Soc., Chem. Commun.
1977,
233
2d Baldwin JE.
Thomas RC.
Kruse LI.
Silberman L.
J. Org. Chem.
1977,
42:
3846
3 Forest J.
Bee C.
Cordaro F.
Tius MA.
Org. Lett.
2003,
5:
4069
4 Dhoro F.
Tius MA.
J. Am. Chem. Soc.
2005,
127:
12472
5 Hashmi ASK.
Bats JW.
Choi J.-H.
Scharz L.
Tetrahedron Lett.
1998,
39:
7491
6a Loupy A.
Top. Curr. Chem.
1999,
206:
153
6b Tanaka K.
Solvent-Free Organic Synthesis
Wiley-VCH;
Weinheim:
2003.
7 Professor Marvin J. Miller (Notre Dame) had suggested that a trace metal oxide present as a contaminant in silica gel, possibly iron, was responsible for catalyzing the cyclization reaction. The silica gel manufacturer’s (Natland International Corporation) certificate of analysis indicated ‘less than 0.02% iron’ (<200 ppm) and our independent determination (Desert Analytics) indicated 0.03% (300 ppm) iron. Iron is certainly present, probably as Fe(III) oxide; therefore we cannot exclude this possibility.
8a Habermas KL.
Denmark S.
Jones TK.
Org. React.
1994,
45:
1
8b Tius MA.
Acc. Chem. Res.
2003,
36:
284
8c Harmata M.
Chemtracts
2004,
17:
416
8d Frontier A.
Collison C.
Tetrahedron
2005,
61:
7577
8e Pellissier H.
Tetrahedron
2005,
61:
6479
8f Tius MA.
Eur. J. Org. Chem.
2005,
2193
9 Ding G.
Song YC.
Chen JR.
Xu C.
Ge HM.
Wang XT.
Tan RX.
J. Nat. Prod.
2006,
69:
302
