Synthesis of Acylsilanes by Palladium-catalyzed Cross-coupling Reaction of Thiol Esters and Silylzinc Chlorides

Abstract

An acylsilane synthesis by a Pd-catalyzed cross-coupling reaction of thiol esters and silylzinc chlorides was developed. S-Phenyl thiol esters with a variety of functional groups were converted to corresponding acylsilanes.Since acylsilanes possess a variety of unique reactivities, 1 their synthesis has been an important research topic in organic chemistry.1p1r,24 Brook 2a and Corey 2b independently reported representative methods to prepare acylsilanes by silylation of a lithiated dithiane followed by removal of dithiane. Acylsilanes are also synthesized by 1,2-addition of silyllithium to aldehydes followed by oxidation according to a procedure of Reich. 5However, both methods have only limited functional group compatibility since they use strong bases such as n-BuLi. To circumvent these problems, palladium-catalyzed cross-coupling of acid chlorides with disilane 4a4d or stannylsilane 4e has recently been reported. These methods, however, are unsatisfactory because they require harsh conditions such as heating at high temperature without solvent. On the other hand, thiol esters are a suitable substrate for cross-coupling reactions based on oxidative addition of a transition-metal catalyst to the CS bond. 6,7 Under this background, we initiated a study of the transformation of thiol esters to acylsilanes. Herein, we report a mild synthesis of acylsilanes by palladium-catalyzed crosscoupling of thiol esters and silylzinc chlorides.Based on the proposed reaction mechanism for the palladium-catalyzed cross-coupling reaction of thiol esters with organozinc reagent (Scheme 1), we considered a working hypothesis for transformation of thiol esters to acylsilanes as shown in Scheme 2. Oxidative addition of palladium(0) to the CS bond of the thiol ester gives acyl palladium species which should be transformed to the acylsilane via transmetalation with a silyl metal reagent followed by reductive elimination with regeneration of Pd(0).With this idea in mind, we explored a suitable silyl metal reagent for the expected cross-coupling reaction. Using thiol ester 1a as the model substrate, various silyl metal reagents 4,8

Activator‐Free Palladium‐Catalyzed Silylation of Aryl Chlorides with Silylsilatranes

“…Indeed, lithium chloride as an additive promoted the silylation (eqs 2 and 3), probably through halide ligand exchange between arylpalladium bromide or triflate and lithium chloride. We confirmed this ligand exchange process by 31 P NMR analysis (See Supporting Information). 3 [b] 4-AcHN A 2c…”

“…1 H NMR (600 MHz), 13 C NMR (151 MHz), 31 P NMR (243 MHz), and 29 Si NMR (119 MHz) spectra were taken on a JEOL ECA-600 spectrometer. Chemical shifts were reported as delta scale in ppm relative to CHCl3 (δ = 7.26) for 1 H NMR, to CDCl3 (δ = 77.16) for 13 C NMR, to H3PO4 (δ = 0.00) for 31 P NMR, and to tetramethylsilane (δ = 0.00) for 29 Si NMR. Spectroscopic grade solvents were used for all spectroscopic studies without further purification.…”

Katalyse – ein allgegenwärtiges Prinzip

“…Ethoxysilatrane (6.58 g, 30 mmol) and THF (40 mL) were added to a reaction flask under an atmosphere of nitrogen. Trimethylsilyllithium31 (≈0.24 M in THF, 62 mL, 15 mmol) was added to the solution by cannula. The mixture was stirred overnight at room temperature.…”

Recent Advances in the Synthesis of Acylsilanes

“…[1h,31] In 2011, an efficient method for the preparation of acylsilanes via palladium-catalyzed cross-coupling of thiol esters and silylzinc chloride was achieved by Tokuyama and co-workers (Scheme 21). [32] Under optimal conditions, thiol esters containing various functional groups were tolerated to form the corresponding acylsilanes in high yields. The plausible reaction mechanism is similar to the palladium-catalyzed cross-coupling reaction of thiol esters with organozinc reagents.…”

“…Various carboxylic acid derivatives, for instance, ester, amide, acyl chloride can be used for this silylation process . In 2011, an efficient method for the preparation of acylsilanes via palladium‐catalyzed cross‐coupling of thiol esters and silylzinc chloride was achieved by Tokuyama and co‐workers (Scheme ) . Under optimal conditions, thiol esters containing various functional groups were tolerated to form the corresponding acylsilanes in high yields.…”