Ynolates from the Reaction of Lithiosilyldiazomethane with Carbon Monoxide. New Ketenylation Reactions

Abstract

Ynolates are the triple-bond version of enolates. In contrast to the well-established chemistry of enolates, 1 only scattered examples of the ynolate chemistry have been reported so far. 2-6 The first example was reported in 1975 by Schöllkopf, who succeeded in the generation of lithium phenylethynolate by extrusion of benzonitrile from 5-lithio-3,4-diphenylisoxazole. 2 Since then, various routes to ynolates have been developed by Kowalski, 3 Stang, 4 Julia, 5 and Rathke. 6 Nevertheless, ynolates received only little attention as synthetic reagents because of lack of convenient methods of their generation. The reactions of ethynolates with aldehydes, 2a,b,3a ketones, 2a,b,3a and imines 2c to give the corresponding -lactones or -lactams have been studied. A silylethynolate 6 is quite attractive because a silyl group can be converted into other functional groups in various ways. 7 In this paper a unique access to and the new reactions of the silylethynolate will be described.Our new route to the lithium silylethynolate involves the acyllithium (R-CO-Li) chemistry. Two different approaches have been developed to utilize the highly reactive intermediate RCOLi. The one involves in situ intermolecular trapping of the acyllithium as studied by Seyferth 8 and others. 9 The other developed by us involves intramolecular conversion of the unstable acyllithium to a more stable but still useful intermediate such as enolate. 10 Now we have studied the reaction of a lithiated silyldiazomethane 1 with carbon monoxide expecting that the extrusion of dinitrogen from an acyllithium 2 should provide the driving force for a clean reaction. This is the case. The results not only provide a unique entry to a lithium ynolate having a silyl group 6 4 (Scheme 1) but also lead to a unique synthetic operation that enables "ketenylation". 11 To a THF-hexane solution of trimethylsilyldiazomethane 12 was added a hexane solution of BuLi (1.2 equiv) at -78°C and the mixture was stirred at that same temperature for 1 h. Then, the mixture was exposed to an atmospheric pressure of carbon monoxide at -78°C for 2 h. Addition of 1.

A Solid‐State, Solution, and Theoretical Structural Study of Kinetic and Thermodynamic Lithiated Derivatives of a Simple Diazomethane and Their Reactivities Towards Aryl Isothiocyanates

“…[19] X-Scheme 3. Proposed pathways for the reaction of different 1-Li isomers with RNCS (R ϭ Ph, Bz) [12,18] ray crystallography has shown 1-Li· 3 / 2 THF to be a polymer based on a repeating tetramer unit (Figure 4) ) which collapse to a single set upon hydrolysis to 1-H. The ambiguity surrounding the preferred site of lithiation in 1-H that results from the contrasting structures noted for 1-Li· 3 / 2 THF and 7 made it desirable to theoretically probe the relative stabilities and geometries of both N-and C-lithiates.…”

“…[1] However, we report here that (for R ϭ Bz) such a reaction, if followed by reflux and the addition of TMEDA affords S-lithio-1-benzyl 4-trimethylsilyl-5-thio-1,2,3-triazole, BzNNNC(Me 3 Si)C(SLi·TMEDA) (12) as the only isolable product. In the solid state 12 is dimeric (Figure 13) and consists of two (mono-TMEDA) complexed metallo-1-benzyl-5-thio-4-trimethylsilyl-1,2,3-triazole molecules.…”

“…[17] This species is composed both of 6 and lithiotriazole 8, this last component evidently being formed by the reaction of 6 with 1-H. Suggestions [12,18] that the reactivity of lithiated 1-H is solvent dependent have been borne of the observation that whereas it reacts with RNCS (R ϭ alkyl, aryl) in OEt 2 to afford 2-amino-1, 3,4-thiadiazole (13), in THF thio-1,2,3-triazoles 10Ϫ12 result (Scheme 3). [18b] However, such difScheme 2.…”

“…[12] These last species react with phosphorus ylides and so afford a simple route to silyl allenes. [13] In this context, central to the synthesis [13] of the disubstituted silyl ketene 3, is the formation, by the sequential treatment of 1-H with n-butyllithium and carbon monoxide, of a lithium ynolate 2.…”

“…Summary of DFT calculations (B3LYP/6-311G**) [21,22] lation as external solvation increases; an important inference given the previously reported reactivities of lithiated (trimethylsilyl)diazomethanes in different Lewis base media. [12,18] Differences in the calculated energies of the variously coordinated mono-solvates do not, however, translate into significant differences in bonding parameters. Slight changes are noticeable relative to unsolvated III and IV on the inclusion of Lewis base and this is most apparent in increments to CϪLi lengths (to, 1.959 and 1.956 Å for V and VII, respectively, cf.…”