Stille reaction

The Stille reaction, or the Migita–Kosugi–Stille coupling, is a chemical reaction widely used in organic synthesis which involves the coupling of an organotin compound (also known as organostannanes) with a variety of organic electrophiles via palladium-catalyzed coupling reaction. The R1 group attached to the trialkyltin is normally sp2-hybridized, including alkenes, and aryl groups; however, conditions have been devised to incorporate both sp3-hybridized groups, such as allylic and benzylic substituents, and sp-hybridized alkynes. These organostannanes are also stable to both air and moisture, and many of these reagents either are commercially available or can be synthesized from literature precedent. However, these tin reagents tend to be highly toxic. X is typically a halide, such as Cl, Br, or I, yet pseudohalides such as triflates and sulfonates and phosphates can also be used. The groundwork for the Stille reaction was laid in 1976 and 1977 by Colin Eaborn, Toshihiko Migita, and Masanori Kosugi, who explored numerous palladium catalyzed couplings involving organotin reagents. John Stille and David Milstein developed a much milder and more broadly applicable procedure in 1978. Stille's work on this area might have earned him a share of the 2010 Nobel Prize, which was awarded to Richard Heck, Ei-ichi Negishi, and Akira Suzuki for their work on the Heck, Negishi, and Suzuki coupling reactions. However, Stille died in the plane crash of United Airlines Flight 232 in 1989. Several reviews have been published on the Stille reaction. The first example of a palladium catalyzed coupling of aryl halides with organotin reagents was reported by Colin Eaborn in 1976 (A). This reaction yielded from 7% to 53% of diaryl product. This process was expanded to the coupling of acyl chlorides with alkyl-tin reagents in 1977 by Toshihiko Migita, yielding 53% to 87% ketone product (B). Later in 1977, Migita published further work on the coupling of allyl-tin reagents with both aryl (C) and acyl (D) halides. The greater ability of allyl groups to migrate to the palladium catalyst allowed the reactions to be performed at lower temperatures. Yields for aryl halides ranged from 4% to 100%, and for acyl halides from 27% to 86%. After this groundwork was laid, Stille reported the coupling of a variety of alkyl tin reagents in 1978 with numerous aryl and acyl halides with much more mild reaction conditions, with much better yields (76%-99%). Stille continued his work in the 1980s on the synthesis of a multitude of ketones using this broad and mild process and elucidated a mechanism for this transformation. By the mid-1980s, over 65 papers on the topic of coupling reactions involving tin had been published, continuing to explore the substrate scope of this reaction. While initial research in the field focused on the coupling of alkyl groups, most future work involved the much more synthetically useful coupling of vinyl, alkenyl, aryl, and allyl organostannanes to halides. Due to these organotin reagent's stability to air and their ease of synthesis, the Stille reaction became commonly used in organic synthesis.