Cobalt Carbonyl Catalyzed Reactions of Cyclic Ethers with a Hydrosilane and Carbon Monoxide. A New Synthetic Reaction Equivalent to Nucleophilic Oxymethylation

Article abstract of DOI:10.1021/ja00202a040

Siloxymethylative ring opening of cyclic ethers has been attained by a new catalytic system of HSiR3/CO/Co2(CO)8.The reaction generally proceeded at room temperatures under 1 atm of CO.The carbon monoxide was incorporated into the product as a part of siloxymethyl group.The reactivity of cyclic ethers decreased in the order of 4 > 3 > 5 >> 6 and 7 membered ring.Among the hydrosilanes (HSiMe3, HSiEt2Me, and HSiEt3), the highly reactive HSiMe3 allowed the use of lower reaction temperature leading to high product selectivities.The regiochemical course of the reactiondepended on the substituents of the oxiranes.The reaction of monosubstituted oxiranes having electron-withdrawing groups, such as hydroxy, acetoxy, and benzoyloxy, resulted in a highly regioselective ring opening at the primary carbon center.While tert-butylethylene oxide reacted at the primary carbon, styrene oxide reacted at the secondary center.The stereochemical course of the reaction was demonstrated to be trans in the cases of cycloalkene oxides and cis- and trans-2-butene oxides.The regio- and stereoselective ring opening of allylic alcohol epoxide derivatives has been attained when their hydroxy group was converted into monochloroacetoxy group.Rare examples of incorporation of carbon monoxide into tertiary carbon centers were observed for the ring opening of geminal dialkyl-substituted oxiranes.The importance of R3SiCo(CO)4 (3) as a key catalyst species and the reaction mechanism have been discussed.An acylcobalt carbonyl intermediate generated by the stoichiometric reaction of R3SiCo(CO)4 (3) with tert-butylethylene oxide was intercepted by a 1,3-diene.