Functionalisation of Alkylalkoxysilanes. Studies Towards Annulations of Diterpenoids
摘要:
Ortho-(2-triethoxysilylethyl) derivatives of aryl ketones undergo oxidative desilylation with H2O2. Tetralone derivatives have served as model substrates for 14-2-(triethoxysilylethyl)-7-oxopodocarpanes, which have been converted into 2-arylethanols in a four-step sequence (BH3. BMS, H2O2, Et3SiH/CF3COOH, TBAF) without isolation of intermediate products (oxasilepin, diol, trifluoroacetate). Use of the 14-(2-diethoxysilylmethyl) analogue improved the overall yield significantly (75 versus 40%). Re-oxidation of ring B with CAN gave the Delta(5)-7-oxo derivative, which was converted into an enone-aldehyde by treatment with Collins' reagent. The conjugated alkene was reduced stereoselectively with SmI2, which, however, did not promote pinacol coupling of the resulting 1,5-keto aldehyde. (C) 2000 Elsevier Science Ltd. All rights reserved.
To obtain further insight into the new ruthenium-catalyzed reaction of carbon–hydrogenbonds in aromatic ketones with olefins, the effect of various substituents at the aromatic ring is examined. Reaction of o-methylacetophenone with triethoxyvinylsilane (2) in the presence of [Ru(H)2(CO)(PPh3)3] (3)as the catalyst gave the 1 : 1 addition product in quantitative yield. Similarly, the ketone having
Effective conditions for the hydroarylation of vinylsilanes, allowing functionalization of various aromatic ketones in good yields at low temperature, using isopropanol, a protic solvent, are reported. Moreover, conducting this C−C bond-forming reaction under conditions similar to those used for hydride transfer reduction, the reduction of the ketone could be suppressed, simply by using acetone cosolvent
Ru(H)2(CO)(PPh3)3, have been found to catalyze the addition of ortho C–H bonds of aromatic ketones to olefins with a high degree of efficiency and selectivity. 2′-Methylacetophenone reacts with various types of terminal olefins to give 1 : 1 coupling products in good to excellent yields. The C–C bond formation takes place exclusively at the terminal carbon atom of olefins except for styrene which affords a mixture
A very simple and efficient catalytic system for the hydroarylation of olefins by aromatic ketones and Michael acceptors using simple and inexpensive ruthenium trichloride as a ruthenium source is described. These very mild conditions (dioxane at 80 C) appeared to be highly compatible, tolerant, and selective toward various functional groups, and the ease of the protocol is highly convenient for synthetic purposes.