(2 E )‐3‐(Tributylstannyl)‐2‐propenoic acid

Abstract

[202115-93-3] C15H30O2Sn (MW 361.11) InChI = 1S/3C4H9.C3H3O2.Sn/c3*1-3-4-2;1-2-3(4)5;/h3*1,3-4H2,2H3;1-2H,(H,4,5); InChIKey = LRBBOPJETNHLHJ-UHFFFAOYSA-N Alternative Name: (E)-β-tributylstannylacrylic acid. Physical Data: colorless, viscous oil. IR (neat): 1690, 1624, 1570 cm–1. 1H NMR (200 MHz, CDCl3): d = 0.93 (t, J = 7.2 Hz, 9H), 1.02 (m, 6H), 1.23–1.62 (m, 12H), 6.36 (d, J = 19.4 Hz, JSn–H = 54–51 Hz, 1H), 7.93 (d, J = 19.4 Hz, JSn–H = 58 Hz, 1H), 10.70 (br s, 1H). 13C NMR (50 MHz, CDCl3): d = 9.6 (JSn–C = 335–351 Hz, 3 C), 13.5, 27.1 (JSn–C = 57–55 Hz, 3 C), 28.8 (JSn–C = 21 Hz, 3 C), 135.6 (JSn–C = 13 Hz), 156.4 (JSn–C = 292–283 Hz), 169.6 (JSn–C = 69 Hz) 119Sn NMR (149 MHz, CDCl3) δ −45.5.1 Solubility: the free acid is soluble in many organic solvents, and the corresponding (alkali metal) salts are water soluble. Analysis of Reagent Purity: 1H, 13C, and 119Sn NMR spectroscopy. Preparative Methods: a direct method to access (2E)-3-(tributylstannyl)-2-propenoic acid is stannyl cupration of propiolic acid, which leads to the isomerically pure product.1,2 Alternatively, alkaline hydrolysis of various esters affords the parent acid with complete retention of the olefin geometry (eq 1). Said esters can be obtained either by analogous stannyl cupration3 or via free-radical hydrostannylation of the propiolic acid derivatives.4,5 The latter method leads to mixtures of the geometrical isomers; however, these are readily separable by flash chromatography. The corresponding Z-isomer can be converted to (Z)-β-tributylstannylacrylic acid analogously.6 (1) Purification: (E)-β-tributylstannylacrylic acid is quite stable to acidic and alkaline conditions, which allows for a straightforward acid/base extraction to remove uncharged or basic impurities. Flash chromatography on silica gel is also possible as no appreciable protodestannylation occurs, but as an unprotected carboxylic acid, 1 tends to streak considerably. Handling, Storage, and Precautions: as most organotin compounds, the title compound is very likely toxic. Any ingestion or skin contact has to be avoided. Since it displays no appreciable vapor pressure, the compound can be safely handled if sufficient protective measures (e.g., goggles, gloves, lab coat, and fume hood) are taken. General Reactivity: (2E)-3-(tributylstannyl)-2-propenoic acid presents a useful building block in organic synthesis. It features carboxylic acid and vinyl stannane termini as orthogonal sites of reactivity. This allows for the straightforward elaboration in either direction, which has been demonstrated in several total syntheses of natural products. In this context, the exceptional mildness of Stille compared to, e.g., Heck or Suzuki couplings, which require additional base and sometimes elevated temperatures, is an important asset. Moreover, if a β-electrophilic acrylate synthon is desired, facile and stereospecific iododestannylation gives access to either (E)-β-iodoacrylic acid or the corresponding esters.