188017-81-4Relevant academic research and scientific papers
Camphor-derived, chelating auxiliaries for the highly diastereoselective intermolecular Pauson-Khand reaction: Experimental and computational studies
Verdaguer, Xavier,Vazquez, Jordi,Fuster, Gerard,Bernardes-Genisson, Vania,Greene, Andrew E.,Moyano, Albert,Pericas, Miquel A.,Riera, Antoni
, p. 7037 - 7052 (2007/10/03)
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 lOb-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 °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 lOb with norbornadiene, 14, has been used as the starting point for a synthesis of (S)-(-)-4-alkyl-2-cyclopentenones through a se'quence 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.
Optically pure alkoxychlorosulfuranes. Synthesis and transformation to chiral sulfoxides, N-p-tosylsulfilimines, and sulfonium ylides
Zhang, Jian,Takahashi, Tamiko,Koizumi, Toru
, p. 325 - 339 (2007/10/03)
Optically pure alkoxychlorosulfuranes (1) have been prepared by using the 2-exo-hydroxy-10-bornyl group as a chiral ligand. The structure of sulfurane (1a) was confirmed by 1H-nmr, 13C-nmr, and mass spectra. Nucleophilic reaction of
Enantioface-differentiating protonation with chiral γ-hydroxyselenoxides
Takahashi, Tamiko,Nakao, Naoki,Koizumi, Toru
, p. 3293 - 3308 (2007/10/03)
Enantioface-differentiating protonation of a chiral metal enolates of α-alkylcarbonyl compounds 7 has been developed using chiral γ-hydroxyselenoxides 1 as a proton source. Reaction of zinc bromide enolates of 2-benzyl- and 2-n-propylcyclohexanones with (S(Se))-1e gave (S)-2-benzylcyclohexanone 7a and (R)-2-n-propylcyclohexanone 7c in high enantiomeric excess, respectively. Intramolecular hydrogen bonding of the selenoxide 1, chelation effects between 1 and metal enolate, and 2-exo-hydroxy-10-bornyl-framework could contribute to this asymmetric induction.
