Conversion of some alkenyltrimethylsilanes into silyl enol ethers
作者:Robert F. Cunico
DOI:10.1016/s0022-328x(00)85675-2
日期:1981.6
The cycloaddition products (5-trimethylsilylisoxazolines) between alkenyltrimethylsilanes and acetonitrile oxide undergo thermolytic rearrangement-cycloreversion to afford silyl enol ethers of retained stereochemistry vs. the starting alkenylsilanes.
On the origin of geminal regioselectivity in the ene reaction of singlet oxygen with substituted alkenes
作者:Waldemar Adam、Markus J. Richter
DOI:10.1016/s0040-4039(00)61349-7
日期:1993.1
The geminal regioselectivity observed in the ene reaction between singletoxygen and alkenes with anion-stabilizing groups is rationalized on the basis of a perepoxide intermediate, in which in analogy to the nucleophilic attack on protonated epoxides, the perepoxide is opened preferentially at the CO bond weakened by the substituent.
Regioselectivity of the Singlet Oxygen Ene Reaction (Schenck Reaction) with Vinylsilanes
作者:Waldemar Adam、Markus J. Richter
DOI:10.1021/jo00091a020
日期:1994.6
The ene reaction-of singlet oxygen and vinylsilanes 1 with various substitution patterns and double-bond geometry has been studied. beta-Silyl allylic hydroperoxides 2 were the major products of the photooxygenation, accompanied by smaller amounts of alpha,beta-unsaturated ketones 3. The latter derive from decomposition of the regioisomeric alpha-hydroperoxy silanes 4 by elimination of silanol. Regioselectivities up to 97:3 were observed for vinylsilanes with a methyl group geminal to the silyl group and with cyclic derivatives. Z-Configurated substrates showed lower regioselectivity and reactivity. Elongation of the carbon chain at the geminal position also increased the amount enone formed. These results are rationalized in terms of stereoelectronic effects imposed by the silyl group on the ring-opening of the perepoxide intermediate.
Highly Regio- and Diastereoselective One-Pot Synthesis of Silyl Epoxy Alcohols and Vinylsilanes by Direct Hydroxy-Epoxidation
作者:Waldemar Adam、Markus J. Richter
DOI:10.1021/jo00091a021
日期:1994.6
A direct synthesis of silyl epoxy alcohols from vinyl silanes is described. It consists of the regioselective ene reaction of the vinylsilanes with singlet oxygen, which proceeds with predominant hydrogen abstraction at the position geminal to the silyl group. The resulting silyl allylic hydroperoxides were treated, without isolation, subsequently with Ti(O-i-Pr)(4) to afford the silyl epoxy alcohols in good yields and very high diastereomeric ratios, which ranged from 93:7 to greater than 97:3. Alternatively, the vinylsilanes were photooxygenated directly in the presence of the titanium catalyst and the silyl epoxy alcohols obtained in good yields. The method was applied to di- and trisubstituted acyclic vinylsilanes with a methyl group geminal to silicon and cyclic derivatives all give consistently good results. In this novel hydroxy-epoxidation, the regioselectivity of the singlet oxygen ene reaction as well as the diastereoselectivity of the oxygen transfer can be controlled by the steering effects of the silyl group.
Formation of α-silylvinyllithium reagents: Reactions of α-silyl- and α-stannyl-vinyllithiums with aldehydes and ketones