Additions of benzylsulfonium ylides to aldehydes and ketones: are they under kinetic or thermodynamic control?

Aggarwal, Varinder K.; Calamai, Simone; Ford, J. Gair

doi:10.1039/a606925h

Cited by 57 publications

(46 citation statements)

References 12 publications

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“…The aromatic nature of the ferrocenyl substituent favors kinetic control leading to trans and cis mixtures. This stands in contrast to dialiphatic sulfides for which Aggarwal and co-workers have shown 42 that the formation of the syn betaine, leading to cis oxiranes is reversible. The anti betaines were formed irreversibly and the trans oxiranes were predominantly obtained.…”

Section: Discussionmentioning

confidence: 99%

Synthesis of planar chiral ferrocenyl sulfides and evaluation as catalysts for the asymmetric epoxidation of aldehydes

Minière¹,

Reboul

Metzner³

2005

Arkivoc

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New ferrocenyl sulfides, exhibiting planar chirality, have been prepared. They incorporate various heteroatom groups, and in some cases central chirality (sulfur or carbon). They were evaluated as catalysts for the asymmetric epoxidation of aldehydes via sulfonium ylides. A onepot reaction has been achieved, involving addition of benzaldehyde, benzyl bromide, 20% molar equivalent of the ferrocenyl sulfide, sodium iodide in a mixture of tert-butanol and water. Good yields of stilbene oxide were obtained, with enantiomeric excesses up to 53%.

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Section: Discussionmentioning

confidence: 99%

Synthesis of planar chiral ferrocenyl sulfides and evaluation as catalysts for the asymmetric epoxidation of aldehydes

Minière¹,

Reboul

Metzner³

2005

Arkivoc

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“…3). Then, if formation of the betaines is reversible, 24 the ring closure step will determine the diastereoselectivity leading to trans-products (exclusively or major), which is usually the case for arylepoxides and the cis epoxides, when formed, should have the (1S,2R)configuration.…”

Section: Resultsmentioning

confidence: 99%

Trans‐diaryl epoxides: Asymmetric synthesis, ring‐opening, and absolute configuration

et al. 2004

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Anthryl-phenyl, phenanthryl-phenyl, and naphthyl-phenyl trans-epoxides (1, 2, and 3, respectively) having enantiomeric purities of 95%, 99%, and 96% were synthesized from a diastereo and enantiopure sulfonium salt derived from Eliel's oxathiane. The determination of their (1R,2R) absolute configurations was achieved by application of the CD exciton chirality method using a Zn-porphyrin tweezer on the corresponding alcohols obtained after opening of these epoxides with LiAlH(4). The R-configuration at C2 of these epoxides, (-)-1, (+)-2, and (-)-3, is consistent with our previous results concerning asymmetric synthesis of monoaryl epoxides, cyclopropanes, and aziridines. The (1S,2R)-configuration of the cis isomer (when present) was also confirmed. Moreover, the agreement between the negative exciton chirality for conjugates of (S)-configuration predicted by molecular modeling and the observed CD spectra helps to clarify the relative steric size of phenyl and CH(2)-aryl (phenanthryl or anthryl), which is critical when the tweezer method is applied for absolute configurational assignment (phenyl = medium group; anthacenyl CH(2) and phenanthryl CH(2) = large group).

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“…In reactions with benzaldehyde it was found that the trans epoxide was derived from the non-reversible formation of the anti betaine 23, whilst the cis epoxide was generated by the reversible formation of the syn betaine 24 [11]. This productive non-reversible anti betaine formation and unproductive reversible syn betaine formation results in the overall high trans selectivities.…”

Section: Discussion Of Factors Affecting Diastereo-and Enantioselectimentioning

confidence: 97%

Asymmetric Synthesis of Epoxides and Aziridines from Aldehydes and Imines

Aggarwal¹,

Badine²,

Moorthie³

2006

Aziridines and Epoxides in Organic Synthesis

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Epoxides and aziridines are strained three-membered heterocycles. Their synthetic utility lies in the fact that they can be ring-opened with a broad range of nucleophiles with high or often complete stereoselectivity and regioselectivity and that 1,2-difunctional ring-opened products represent common motifs in many organic molecules of interest. As a result of their importance in synthesis, the preparation of epoxides and aziridines has been of considerable interest and many methods have been developed to date. Most use alkenes as precursors, these subsequently being oxidized. An alternative and complementary approach utilizes aldehydes and imines. Advantages with this approach are: i) that potentially hazardous oxidizing agents are not required, and ii) that both C-X and C-C bonds are formed, rather than just C-X bonds (Scheme 1.1).This review summarizes the best asymmetric methods for preparing epoxides and aziridines from aldehydes (or ketones) and imines. Asymmetric Epoxidation of Carbonyl CompoundsThere have been two general approaches to the direct asymmetric epoxidation of carbonyl-containing compounds (Scheme 1.2): ylide-mediated epoxidation for the construction of aryl and vinyl epoxides, and a-halo enolate epoxidation (Darzens reaction) for the construction of epoxy esters, acids, amides, and sulfones.

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Additions of benzylsulfonium ylides to aldehydes and ketones: are they under kinetic or thermodynamic control?

Cited by 57 publications

References 12 publications

Synthesis of planar chiral ferrocenyl sulfides and evaluation as catalysts for the asymmetric epoxidation of aldehydes

Synthesis of planar chiral ferrocenyl sulfides and evaluation as catalysts for the asymmetric epoxidation of aldehydes

Trans‐diaryl epoxides: Asymmetric synthesis, ring‐opening, and absolute configuration

Asymmetric Synthesis of Epoxides and Aziridines from Aldehydes and Imines

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