Ynolates were found to react with alpha-alkoxy-, alpha-siloxy-, and alpha-aryloxyketones at room temperature to afford tetrasubstituted olefins with high Z selectivity. Since the geometrical selectivity was determined in the ring opening of the beta-lactone enolate intermediates, the torquoselectivity was controlled by the ethereal oxygen atoms. From experimental and theoretical studies, the high Z
Trimethylsilyl enol ethers bearing trialkylsilyl-protected hydroxy groups were converted into synthetically valuable bifunctional alkenyl nonaflates under the action of nonafluorobutane-1-sulfonyl fluoride combined with potassium fluoride in the presence of catalytic amounts of dibenzo-18-crown-6. The methodology has been demonstrated for structurally diverse substrates possessing various trialkylsilyl-protected hydroxy groups which remained intact during the reaction course.
Antiproliferative Hybrid Analogs of the Hormone 1α,25-Dihydroxyvitamin D<sub>3</sub>: Design, Synthesis, and Preliminary Biological Evaluation
作者:Gary H. Posner、Jae Kyoo Lee、M. Christina White、Richard H. Hutchings、Haiyan Dai、Joseph L. Kachinski、Patrick Dolan、Thomas W. Kensler
DOI:10.1021/jo970049w
日期:1997.5.1
dichloride promotes highly regioselective and stereoselective Diels-Alder cycloaddition between 3-bromo-2-pyrone, prepared in a new way, and unactivated terminal alkene 4-(tert-butyldimethylsiloxy)-1-butene. The conjugate base of A-ring allylic phosphine oxide 20 adds chemospecifically to the C-8 keto group of some C-8,C-24-diketones to form directly metabolically resistant 24-oxo analogs of 1alpha,25-dihydroxyvitamin
AbstractThe first total synthesis of 1,2‐Dehydronephthenol (15‐hydroxy‐cembra‐1,3,7,11‐tetraene), a novel cembranoid diterpene, was accomplished starting from trans, trans‐farnesol through seven steps in an overall yield of 17% by employing titanium‐induced intramolecular keto aldehyde reductive olefination‐coupling as the key macrocyclization step.