Tin Hydrides and Functional Group Transformations

Abstract

Tin hydrides have played an important role in the development of radical chemistry. Despite their comparatively late discovery as reagents for radical reactions in the late 1950s, they have since then had a tremendous impact. After a short historical introduction including two milestones in tin hydride radical chemistry, an overview is given of the manifold applications tin hydrides are useful for. Starting from the preparation of the classic tin hydrides, new variants are presented along with their advantages over the traditional reagents. In relation to simple radical reductions, for which tin hydrides are popular reagents because of their hydrogen‐donor abilities, we show which functional groups are suited for the tin‐mediated generation of radicals. If those radicals are not immediately reduced by the tin hydride, a large number of group transformations can be performed ranging from simple cyclizations to complex rearrangements or domino reactions.

Radical Cyclizations of Cyclic Ene Sulfonamides Occur with β-Elimination of Sulfonyl Radicals to Form Polycyclic Imines

“…However, the focus of much of this prior work has been on substitution of sulfonyl groups by second-row radicals (especially carbon radicals) rather than tin radicals. In contrast, homolytic substitutions at sulfur atoms in lower oxidation states (for example, ArSR and ArS(O)R) with carbon, tin, and other radicals are common …”

Methodologies Limiting or Avoiding Contamination by Organotin Residues in Organic Synthesis

“…This methodology that allows short reaction times and workups was applied to the synthesis of selectively labeled [ 11 C]methyl quinolines, which are potential tracers for positron emission tomography (PET), using the Lappert-type 11 Cmonomethylstannate 135,136 (Scheme 17).…”

“…Among all tin reagents, trialkyltin hydrides, especially tributyltin hydride, are privileged, as highlighted in a few review articles, ,− as reagents for reductive radical reactions as well as for radical cyclizations. The organotin reagents are also widely used as coupling partners in palladium-catalyzed cross-coupling reactions, mainly for the construction of C sp 2 –C sp 2 bonds according to Stille–Migita cross-coupling. − This reaction allows a good control of the stereochemistry in the resulting vinylic systems and a great functional group tolerance. − Accordingly, some C–C bonds, not that easy to synthesize, as for instance those involving the cross-coupling of “umpolung” organotin reagents with acyl halide, can be obtained, providing for instance highly efficient syntheses of 1,2 or 1,4-dicarbonyl compounds − with possible control of the stereochemistry .…”

Practical metal- and additive-free methods for radical-mediated reduction and cyclization reactions

“…Tin hydride-mediated radical reactions hold a prominent position in organic synthesis. 1 Radical deoxygenation, decarboxylation and dehalogenations as well as diverse reductions and radical cyclization strategies remain as some of the most reliable synthetic tools of an organic chemist. 2 However, despite the high usefulness of tin-hydrides and the reactions they promote, excessive employment of these reagents is nowadays discouraged.…”