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

Consecutive Three‐Component Synthesis of Ynones by Decarbonylative Sonogashira Coupling

“…[9] Palladium complexes are not commonly used for decarbonylations. Besides decar-bonylative carbostannylations, [10] Gooßen has reported decarbonylative Heck reactions with reaction times of 16 h at 160 8C in NMP as a solvent. [11] Just recently, the same group has introduced Pd/Cu-catalyzed decarboxylative cross-couplings of a-oxocarboxylates with aromatic bromides [12] and chlorides [13] at high temperatures and long reaction times.…”

Ruthenium‐Catalyzed Alkene Synthesis by the Decarbonylative Coupling of Aldehydes with Alkynes

“…[10] The process contrasts with hydroacylation reactions in which the carbonyl group is retained. [11] The only previous report of an intermolecular decarbonylative addition to alkynes involves the use of acylstannanes to give vinylstannane products catalyzed by Pd/C. [12] After a thorough screening of catalyst combinations, the reported system of 10 mol % [{Ru(cod)Cl 2 } n ], 30 mol % CuCl 2 ·2 H 2 O, and five equivalents LiCl was found to give the best conversions.…”

Synthesis of Trisubstituted Alkenylstannanes through Copper‐Catalyzed Three‐Component Coupling of Alkylboranes, Alkynoates, and Tributyltin Methoxide

“…Additionally, sp 3 -alkylstannanes have not been used for the introduction of alkyl groups. [5] Furthermore, the regioselectivity is not always reliable, especially as the regiocontrol is generally difficult even with alkynes that are desymmetrized by electronic effects.…”