[64724-29-4] · C16H25OSn · 1-Ethoxy-2-tributylstannylethylene · (MW 362.89)
(versatile synthon for acetaldehyde anion)
Physical Data: bp 110 °C/0.3 mmHg.3a
Solubility: sol THF, DMF, MeCN.
Purification: by distillation.3a
Handling, Storage, and Precautions: organostannane reagents are potentially toxic;4 their preparation and use must therefore be conducted wearing appropriate protective clothing in a well ventilated hood. The reagent should be stored under an inert atmosphere and protected from light and moisture.
Treatment of 1-ethoxy-2-tributylstannylethylene (1) with n-Butyllithium proceeds quantitatively to afford (E)-2-ethoxyvinyllithium.3 This reagent exhibits reactivity typical of vinyllithium reagents, affording entry into a variety of substituted enol ethers which are readily hydrolyzed to the corresponding acetaldehyde derivative.3 For further discussion of this chemistry, see 1-Ethoxyvinyllithium.
Stille et al. pioneered the palladium-catalyzed cross-coupling reaction of organostannanes with a variety of electrophilic partners. These reactions proceed under mild conditions which are often compatable with typically sensitive functional groups.1
Aromatic halides, with the exception of phenols and unsubstituted anilines, couple smoothly with (1) to afford the corresponding (Z)-enol ether (eq 1).5 Heteroaromatic halides and triflates also react smoothly with (1).5,6 In several cases, mixtures of (E)- and (Z)-enol ethers were obtained with electron-deficient heteroaromatic substrates.5b,6 Coupling of (1) with an ortho heterosubstituted aromatic substrate followed by hydrolysis to the acetaldehyde and cyclization is a convenient and flexible method for the preparation of functionalized heterocycles (eq 2).5b Benzofurans, indoles, isocoumarins, pyranopyridinones, and pyrrolopyridines have been prepared using this sequence.5b
Palladium-catalyzed carbonylative coupling of (1) with aromatic iodides affords (E)-3-ethoxy-1-phenyl-2-en-3-ones in moderate yield.7 Under similar coupling conditions the corresponding aryl bromides yield none of the expected product. Electron-deficient aromatic systems are poor substrates for this reaction. In such cases the rate of direct insertion of (1) is competitive with the carbonylative coupling reaction. For example, carbonylative coupling of (1) with 4-nitroiodobenzene afforded (E)-3-ethoxy-1-(4-nitrophenyl)prop-2-en-1-one and (Z)-2-ethoxy-1-(4-nitrophenyl)ethylene in 25% and 40% yields, respectively. Chromones and 4(1H)-quinolones have been prepared from these intermediates (eq 3).7
Alfred P. Spada
Rhône-Poulenc Rorer Central Research, Collegeville, PA, USA