The thiopyran route to polypropionates revisited: Selective syn and anti aldol reactions via 3,6-dihydro-4-trimethylsilyloxy-2H-thiopyran
摘要:
Aldol reaction of the amine free Li enolate of tetrahydro-4H-thiopyran-4-one with 1,4-dioxa-8-thiaspiro[4.5]decane-6-carboxaldehyde gives mainly the 2,3-anti-3,4-syn aldol(7:1) in good yield; reaction of the LDA generated lithium enolate proceeds poorly. Using the trimethylsilyl enol ether and TiCl4 gives the 2,3-syn-3,4-syn aldol(>10:1). The adducts can be used for polypropionate synthesis. (C) 1997 Elsevier Science Ltd.
Proline-Catalyzed Ketone-Aldehyde Aldol Reactions are Accelerated by Water
作者:Petri Pihko、Annika Nyberg、Annina Usano
DOI:10.1055/s-2004-831296
日期:——
Proline-catalyzed aldol reactions between acetone or 4-thianone and different aldehydes are accelerated by addition of 1-10 equivalents of water to the reaction medium, allowing stoichiometric aldol reactions to proceed at acceptable rates.
Chiral phosphine oxide successfully catalyzed the direct aldol-type reactions of cyclohexanone derivatives and benzaldehyde derivatives in high stereoselectivities. The reaction mechanism involves the in situ formation of trichlorosilyl enol ethers. The present reaction could be extended to the cross-aldolreactionsbetween two aldehydes.
[reaction--see text] A variety of aldol adducts (i.e., 3-hydroxy ketones) are shown to undergo syn-anti isomerization in the presence of imidazole by an enolizationmechanism with negligible retroaldol or elimination products.
Proline-catalyzed asymmetric aldol reactions of tetrahydro-4H-thiopyran-4-one with aldehydes
作者:Dale E. Ward、Vishal Jheengut
DOI:10.1016/j.tetlet.2004.09.061
日期:2004.11
Proline-catalyzed enantioselective direct intermolecular aldol reactions of tetrahydro-4H-thiopyran-4-one with various aldehydes give anti adducts with high diastereo- and enantioselectivities in moderate to excellent yields. With the aromatic aldehydes best results were obtained in wet DMF whereas dry DMSO generally was superior with the aliphatic aldehydes. Desulfurization of the adducts with Raney
Sterically and Electronically Tunable and Bifunctional Organocatalysts: Design and Application in Asymmetric Aldol Reaction of Cyclic Ketones with Aldehydes
tunable and bifunctional organocatalysts have been developed and evaluated in the direct aldolreaction of heterocyclic ketones. Catalysts with different substituents showed variablecatalytic efficiency for analogous substrates, indicating the importance of fine-tuning the strength of the hydrogen bonding in the two NH groups. The reactions all proceeded in good to high yield and with excellent enantioselectivities