Communication
The Phenylsulfonyl Group as an endo Stereochemical Controller in Intramolecular Pauson–Khand Reactions of 3-Oxygenated 1,6-Enynes
Javier Adrio,
Marta Rodríguez Rivero,
Juan C. Carretero Prof.,
Javier Adrio
Departamento de Química Orgánica Facultad de Ciencias Universidad Autónoma de Madrid, 28049 Madrid (Spain) Fax: (+34) 913-973-966.
Search for more papers by this authorMarta Rodríguez Rivero
Departamento de Química Orgánica Facultad de Ciencias Universidad Autónoma de Madrid, 28049 Madrid (Spain) Fax: (+34) 913-973-966.
Search for more papers by this authorJuan C. Carretero Prof.
Departamento de Química Orgánica Facultad de Ciencias Universidad Autónoma de Madrid, 28049 Madrid (Spain) Fax: (+34) 913-973-966.
Search for more papers by this authorJavier Adrio,
Marta Rodríguez Rivero,
Juan C. Carretero Prof.,
Javier Adrio
Departamento de Química Orgánica Facultad de Ciencias Universidad Autónoma de Madrid, 28049 Madrid (Spain) Fax: (+34) 913-973-966.
Search for more papers by this authorMarta Rodríguez Rivero
Departamento de Química Orgánica Facultad de Ciencias Universidad Autónoma de Madrid, 28049 Madrid (Spain) Fax: (+34) 913-973-966.
Search for more papers by this authorJuan C. Carretero Prof.
Departamento de Química Orgánica Facultad de Ciencias Universidad Autónoma de Madrid, 28049 Madrid (Spain) Fax: (+34) 913-973-966.
Search for more papers by this authorFirst published: 11 August 2000
Citations: 33
Financial support of this work by the Ministerio de Educación y Cultura (DGES, project PB96-0021) and Comunidad de Madrid (project 07B/28/1999) is gratefully acknowledged.
Abstract
Unlike the usual exo-selective Pauson–Khand cyclization of allylic-substituted 1,6-enynes, the reaction of 1,6-enynes with γ-oxygenated α,β-unsaturated sulfone structures occurs with high endo stereoselectivity. As the starting enynes are available in enantiopure form and the sulfonyl group can be easily eliminated, this procedure constitutes a stereocomplementary approach to the asymmetric synthesis of bicyclo[3.3.0]oct-1-en-3-ones [Eq. (1)].
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References
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- 6 Vinyl sulfones had never been successfully used in PK reactions. As a related reported precedent, the treatment of divinyl sulfone with alkyne dicobalt complexes did not give the cyclopentenone PK product (I. U. Khand, P. L. Pauson, Heterocycles 1978, 11, 59) in accordance with the accepted behavior of alkenes with electron-withdrawing substituents (see ref. 4).
- 7 To the best of our knowledge, the only reported case of endo selectivity in a PK reaction of an allylic substituted 1,6-enyne concerns a specific 3,4-disubstituted enyne: J. A. Casalnuovo, R. W. Scott, E. A. Harwood, N. E. Schore, Tetrahedron Lett. 1994, 35, 1153. Similarly, for a study of the endo/exo selectivity in 3,4-disubstituted-1,7-enynes, see C. Mukai, J. S. Kim, H. Sonobe, M. Hanaoka, J. Org. Chem. 1999, 64, 6822.
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- 9 Alternatively, the phenyl-substituted alkynes 7 a and 8 a were readily prepared by Sonogashira reaction of the corresponding terminal alkynes 5 a and 6 a with phenyl iodide (Pd(OAc)2 10 mol %, CuI 10 mol %; PPh3 20 mol %, Et3N 200 mol % in benzene at RT; 81 and 75 % yield, respectively).
- 10 Very similar yields and diastereoselectivities were obtained in the thermal PK reaction (CH3CN, 80 °C) of the dicobalt complexes of the enynes 1 and 3.
- 11 The combination TMANO/molecular sieves has been recently reported as an efficient promoter in PK reactions: L. Pérez-Serrano, L. Casarrubios, G. Domínguez, J. Pérez-Castells, Org. Lett. 1999, 1, 1187.
- 12 Except for the free alcohols 1 a and 3 a, which proved to be rather unreactive in PK reactions. For instance, the alkyne dicobalt hexacarbonyl complex of 1 a did not react at all under thermal (CH3CN, 80 °C) or TMANO-promoted conditions (CH2Cl2, RT). A very low yield of PK products 9 a (25 % yield, endo/exo=85/15) was obtained when the reaction was performed in the presence of TMANO and molecular sieves. In this case, instead of the PK cyclopentenone, the main product was the corresponding exocyclic 1,3-diene (see ref. 4).
- 13 As is usual in other 6-substituted bicyclo[3.3.0]octen-3-ones (for example, ref. 2c), the coupling constant between H5 and H6 is a very simple and excellent criterion for stereochemical diagnosis. Thus, J5,6 is much smaller in the endo isomers (J5,6=3.6–4.8 Hz, H5/H6 in cis relationship) than in the exo isomers (J5,6=7.5–10.5 Hz, H5/H6 in trans arrangement). Also, a characteristic trend was observed for the chemical shift of H6 in the C-4 sulfonylated adducts: H6 is significantly more deshielded in the endo isomer than in the exo isomer (see below), in accordance with the strong deshielding effect of the phenylsulfonyl group on the hydrogen atom in the 1,3-parallel arrangement. Additionally, these stereochemical assignments have been confirmed by NOESY experiments on the pairs of isomers endo/exo 9 b and endo/exo 13 c.
- 14 Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-141942. Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: (+44) 1223-336-033; e-mail: [email protected]).
- 15
Recent examples: S. Fonquerna, R. Rios, A. Moyano, M. A. Pericàs, A. Riera, Eur. J. Org. Chem. 1999, 3459, and references therein.
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- 17b J. Adrio, J. C. Carretero, R. Gómez Arrayás, Synlett 1996, 640. Similar conformational preferences have been reported for γ-oxygenated α,β-unsaturated esters, see:
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- 18 In all the studied cases, only the R enantiomer of the (±)-(E)-γ-hydroxy-α,β-unsaturated sulfone was acetylated (J. C. Carretero, E. Domínguez, J. Org. Chem. 1992, 57, 3867).
- 19 Specific rotations: (S)-1 a: [α]=+90.2 (c=0.2, CHCl3).
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