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Camphor-Derived, Chelating Auxiliaries for the Highly Diastereoselective Intermolecular Pauson-Khand Reaction: Experimental and Computational Studies.
- Source :
-
The Journal of organic chemistry [J Org Chem] 1998 Oct 02; Vol. 63 (20), pp. 7037-7052. - Publication Year :
- 1998
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Abstract
- A family of enantiomerically pure (2R)-10-(alkylthio)isoborneols [methylthio (1), neopentylthio (2), phenylthio (3)], specifically designed as chiral auxiliaries suitable for chirality transfer to cobalt in Pauson-Khand reactions, has been synthesized. The dicobalt hexacarbonyl complexes of the alkoxyacetylenes derived from these alcohols (10a-12a) can be converted to the rather stable, internally chelated, pentacarbonyl complexes 10b-12b by treatment with NMO. The intermolecular Pauson-Khand reactions of 10b-12b with strained olefins take place with synthetically useful rates at low temperatures (down to -20 degrees C), with high yields and diastereoselectivities: norbornene (77%; 92:8), norbornadiene (82%; 96:4), bicyclo[3.2.0]hept-6-ene (91%; 93:7). The major diastereomer of the adduct of 10b with norbornadiene, 14, has been used as the starting point for a synthesis of (S)-(-)-4-alkyl-2-cyclopentenones through a sequence consisting of completely diastereoselective conjugate addition, reductive cleavage with recovery (>95%) of the chiral auxiliary, and retro Diels-Alder reaction. The stereochemical course of the reaction of 10b with norbornadiene has been analyzed and rationalized by theoretical means by using a combined semiempirical [PM3(tm)]/density functional theory [VWN-Perdew-Wang 91] approach.
Details
- Language :
- English
- ISSN :
- 1520-6904
- Volume :
- 63
- Issue :
- 20
- Database :
- MEDLINE
- Journal :
- The Journal of organic chemistry
- Publication Type :
- Academic Journal
- Accession number :
- 11672330
- Full Text :
- https://doi.org/10.1021/jo9809985