73178-43-5Relevant articles and documents
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Schaeffer,Baker
, p. 625 (1958)
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Teichmann
, p. 644 (1963)
Organocatalytic asymmetric formal [3 + 2] cycloaddition with in situ-generated N-carbamoyl nitrones
Gioia, Claudio,Fini, Francesco,Mazzanti, Andrea,Bernardi, Luca,Ricci, Alfredo
supporting information; experimental part, p. 9614 - 9615 (2011/02/23)
(Chemical Equation Presented) A novel organocatalytic formal [3 + 2] cycloaddition reaction with in situ generation of N-carbamoyl nitrones is presented. For the first time, N-Boc- and N-Cbz-protected isoxazolidines have been directly obtained as single diastereoisomers in generally high yields and enantiomeric excesses using mild reaction conditions and inexpensive, readily available Cinchona alkaloid quaternary ammonium salts as catalysts. Synthetic manipulations of the products provided highly valuable building blocks such as free isoxazolidines, a N-Boc-1,3-aminoalcohol, and a free δ-lactam. This report represents a pioneering work in the use of N-carbamoyl nitrones as electron-poor 1,3-dipoles and glutaconates as new dipolarophiles in asymmetric catalysis.
Halogenated-2-pyrones in Sonogashira cross-coupling: limitations, optimisation and consequences for GC analysis of Pd-mediated reactions
Fairlamb, Ian J. S.,Lee, Adam F.,Loe-Mie, Faidjiba E. M.,Niemel?, Elina H.,O'Brien, Ciara T.,Whitwood, Adrian C.
, p. 9827 - 9838 (2007/10/03)
The Sonogashira couplings of 4-bromo-6-methyl-2-pyrone (5) with phenylacetylene, mediated by Pd(PPh3)2Cl2 in the presence of a CuI co-catalyst, have been investigated in detail. The concentration of Pd dramatically influences the product yield, with lower Pd-loadings favouring higher conversions and purer cross-coupled product. A post reaction time-dependence in product conversion is seen in samples quenched solely on silica-gel (eluted with CH2Cl2). The effect is mirrored in reactions employing 4-nitro-bromobenzene (14) and to a lesser extent (E) and (Z)-ethyl 3-iodo-2-propenonate (16) under similar conditions. A more efficient quenching system (using excess dppe) has been developed to enable accurate determinations in product conversions. Alternatively, solvent and base (Et3N) removal in vacuo, or quench with saturated aqueous ammonium chloride, prevents further turnover in Sonogashira coupling. An ESI-MS study on samples eluted through silica was undertaken to probe the nature of the soluble Pd/Cu species. The Sonogashira cross-coupling of 4-chloro- and 6-chloro-2-pyrone (18 and 20, respectively) has further been investigated. The former undergoes successful coupling, however the latter decomposes in polar aprotic and protic solvents under standard conditions, through a chlorine substitution process, making Pd-mediated reactions problematic.
