Regio‐ and Stereoselective Decarbonylative Carbostannylation of Alkynes Catalyzed by Pd/C

Abstract

The carbometalation reaction of alkynes allows the simultaneous, stereoselective formation of both carbon-carbon and carbon-metal bonds and provides us with a highly powerful tool for the synthesis of novel organometallic reagents that contain multisubstituted ethenes.[1] In particular, the palladium-or nickel-catalyzed carbostannylation of alkynes affords highly functionalized alkenylstannanes, which undergo various chemoselective transformations, such as the Kosugi-Migita-Stille coupling reaction. [2,3] Alkynyl, allyl, and acylstannanes which reportedly undergo oxidative addition of a CÀSn bond to palladium(0) and nickel(0) complexes, [4] are successfully applied to the carbostannylation reaction, whereas aryl-, alkenyl-, and alkylstannanes are found to be sluggish probably because of their low potential for oxidative addition to low-valent transition-metal complexes.[5, 6] Herein, we report the first examples of aryl-, alkenyl-, and alkylstannylations of alkynes through the decarbonylative addition of acylstannanes [7] catalyzed by Pd/C [Eq.(1)].[8]During our investigation of the acylstannylation of alkynes, we observed that the reaction of benzoyl-(tributyl)stannane (1 a) with propargyl acetate (2 a; 2.0 equiv) using 2.5 mol % of [Pd 2 (dba) 3 ] (dba = dibenzylideneacetone) in Bu 2 O [9] at 50 8C for 12 h gave (E)-2-phenyl-1-(tributylstannyl)propen-3-yl acetate (3 a) in 29 % yield, as estimated by 119 Sn NMR spectroscopic analysis (Table 1, entry 1). The yield increased to 44 % with propargyl benzoate

Development of the Applications of Palladium on Charcoal in Organic Synthesis

“…Both of the allyl furoate functionalities and alkenylstannane in the corresponding products have been shown to undergo the Tsuji–Trost allylation and the Kosugi–Migita–Stille cross‐coupling, respectively [Eq. (16)] …”

“… The proposed catalytic cycle for the regio‐ and stereoselective decarbonylative carbostannylation of alkynes. Redrawn with permission . Copyright 2006, Wiley‐VCH, Weinheim.…”

Carbostannolysis Mediated by Bis(pentamethylcyclopentadienyl)lanthanide Catalysts. Utility in Accessing Organotin Synthons

“…4 In particular, the carbostannylation of alkynes, a process in which a Sn−C bond is added across a CC unsaturation (Scheme 1), is a powerful synthetic tool which simultaneously forms new C−C and C−Sn linkages. 5 The resulting Snfunctionalized alkenes can be readily employed as synthetic building blocks through Stille coupling reactions. 2c,6 Snfunctionalized enynes have particularly significant synthetic utility due to the adjacent conjugation, 5e,i,7 and such building blocks have demonstrated applications in arylation, 8 alkylation, 5b and subsequent cyclization 9 reactions (e.g., Scheme 2).…”

“…After 16 h at room temperature, reaction progress had plateaued, and no further consumption of ethylene was observable over an additional 2 days at room temperature. The product, 6-ethyl-2-(2-trimethyltin)ethylpyridine (5), was characterized by 1 H, 13 C, COSY, and HSQC NMR (see the Supporting Information). HMBC NMR confirms that both ethyl groups are bound to the 2-and 6positions of a single pyridine core.…”

New Three-Component Glyoxylation-Decarbonylative Stille Coupling Sequence to Acyl Heterocycles under Mild Conditions

“…In particular, catalytic decarbonylations are highly desirable and have recently received considerable attention. For instance, palladiumcatalyzed decarbonylative carbostannylations under mild conditions 5 and decarbonylative Heck reactions 6 at high temperatures and long reaction times have been reported. Recently, we established a new decarbonylative Sonogashira coupling of glyoxylyl chlorides, 7 which are in situ generated at room temperature from oxalyl chloride as an easy-to-handle carbon monoxide surrogate.…”