A new method was developed for allylation of 1,3-diketones, ß-keto esters, and malonates. Treatment of those 1,3-dioxo compounds with allyltrimethylsilane (1.3 equiv) in the presence of ceric ammonium nitrate (2.1 equiv) in methanol at room temperature often gave the mono-Callylated products in good to excellent yields (74-98%). These reactions, involving /3-carboradical and /3-carbocationic intermediates, were controlled by a silyl group. Replacement of ceric ammonium nitrate and methanol with manganese(III) acetate (2.4 equiv) and acetic acid afforded siliconcontaining dihydrofurans in high yields at 80 °C.

The influence of silicon on the carbon-carbon bond formation was investigated by use of various silylalkenes to react with ketones. Treatment of an allylsilane (CH2=CHCH2SiMen,Ph"; m + n = 3) with various ketones (20 equiv) in the presence of Mn02 (2.0 equiv) and a drop of acetic acid at 140 °C in a sealed tube produced the corresponding hydrogen atom transfer adducts in 54-85% yields. Performance of the same reactions by replacement of the allylsilane with a vinylsilane (i.e., CH2=CHSiMe3 and CH2=CHSiMeEt2) afforded adducts in 59-75% yields. Furthermore, reaction of diallyldimethylsilane with acetone or 3-methyl-2-butanone under the same conditions afforded 4-(3,3-dimethyl-3-silacyclohexyl)butan-2-one (81%) and 4-(3,3-dimethyl-3-silacyclohexyl)-3,3-dimethylbutan-2-one (65%), respectively. The results indicate that the a-and the /^-electronic effects of a silicon atom promoted the C-C bond formation, while the regioselectivity came from the steric effect of the silyl group.* Recipient of the Federation of Asian Chemical Societies 1992 and 1993 Distinguished Young Chemist Award.* Academia Sinica.

The effect of silicon on C–C bond formation between carbonyl compounds and allyltrimethylsilane was investigated. Treatment of 1,3‐diketones, β‐ketoesters or malonates with allyltrimethylsilane in the presence of ceric ammonium nitrate (CAN) in methanol produced the corresponding allylated products. Furthermore, introduction of Mn(OAc)3 · 2H2O into those reactions for replacement or assistance of CAN afforded silicon‐containing cyclopentanes in 51–75% yields. A sequential process involving allylation, free‐radical cyclization and elimination was also developed by use of CAN/Mn (OAc)3 · 2H2O/Cu(OAc)2 · H2O. Accordingly, β‐ketoesters or malonates were allowed to react with allylsilanes in acetic acid to give silicon‐containing cyclopentanes with an exo methylene unit in 52–71% yields. These reactions involved carbocationic and carboradical intermediates, of which formation and chemical activities were controlled by a β‐silyl group. © 1997 by John Wiley & Sons, Ltd.

Electron-impact-induced fragmentations were performed in the gas phase on δ-silyl aldehydes, ketones, thioketones, carboxylic acids, and acetates. All of these compounds showed significant silyl migration through a transition state with a seven-membered ring. For ketones and acetates, this silyl migration process may overwhelm the McLafferty rearrangement, which involves a transition state with a six-membered ring.