61878-69-1Relevant academic research and scientific papers
METAL SALT-PROMOTED ALDOL REACTION OF SILYL ENOL ETHERS WITH ALDEHYDES
Chini, Marco,Crotti, Paolo,Gardelli, Cristina,Minutolo, Filippo,Pineschi, Mauro
, p. 673 - 676 (2007/10/02)
Simple metal salts such as lithium perchlorate and zinc triflate effectively promote aldol condensation between silyl enol ethers and aldehydes or acetals in non-protic solvents to yield the O-protected aldols in good yields. A slight preference for the syn aldol is observed when a prochiral silyl enol ether reacts with benzaldehyde, a complete syn stereoselectivity being obtained only in the case of the hindered silyl enol ether 14. The method appears to be simple and competitive with other ones previously described.
Synthesis of η1 Oxygen-Bound Rhodium Enolates. Applications to Catalytic Aldol Chemistry
Slough, Greg A.,Bergman, Robert G.,Heathcock, Clayton H.
, p. 938 - 949 (2007/10/02)
Oxygen-bound rhodium enolate complexes are prepared by metathesis of carbonylbis(phosphine)rhodium(I) halides and potassium enolates, 3-6.Rhodium enolates of acetophenone (7), propiophenone (9), ethyl mesityl ketone (10), and ethyl tert-butyl ketone (11) were prepared and fully characterized.Complex 11 condenses with benzaldehyde under a variety of conditions to produce isolable rhodium aldolate complex 12.Cleavage of 12 with trimethylsilyl chloride yields aldol silyl ether and rhodium chloride.Similar treatment of 12 with an enol silane affords the aldol silylether and a rhodium enolate.A catalytic aldol reaction involving enol silanes, silylketene acetals, and benzaldehyde under rhodium catalysis is presented.Deuterium, phosphorus, and carbon NMR were used to demonstrate the intermediacy of rhodium enolates and aldolates in the aldol process and to elucidate the gross mechanistic features of the catalytic cycle.
Acyclic Stereoselection. 7. Stereoselective Synthesis of 2-Alkyl-3-hydroxy Carbonyl Compounds by Aldol Condensation
Heathcock, Clayton H.,Buse, Charles T.,Kleschick, William A.,Pirrung, Michael C.,Sohn, John E.,Lampe, John
, p. 1066 - 1081 (2007/10/02)
The stereochemistry of the aldol condensation of preformed lithium enolates of a variety of ethyl ketones and propionic acid derivatives with aldehydes has been investigated.It is found that certain compounds give completely or nearly completely one diastereomeric enolate and that the stereostructure of the resulting aldol is correlated with the stereostructure of the enolate from which is formed.The observed stereochemistry may be understood in terms of an ordered transition state in which both oxygens are oriented in more or less the same direction.It is shown that the observed stereochemistry is kinetically controlled.In many cases, the initial aldol adduct equilibrates to furnish predominantly a threo isomer.The rate of equilibration varies widely, ranging from very fast at -60 deg C with the propiophenone-benzaldehyde adduct to slow at 25 deg C for the ethyl tert-butyl ketone-benzaldehyde adduct.The equilibration behavior of lithium ketolates is compared with that of zinc ketolates, and some differences are noted.A method for achieving erythro-threo equilibration via a chloral hemiacetal is presented.A new reagent is introduced (trimethylsilyloxy ketone 36) which may be used to stereoselectively homologate an aldehyde to an erythro α-methyl-β-hydroxy acid.As an application of the use of stereoselective aldol condensations in synthesis, (+/-)-ephedrine (48) has been synthesized from benzaldehyde in 71 percent overall yield.
