Acetal-enolether condensation

Synthesis of a,y -ethylenealdehydes via y -alkoxyacetals Acetal-enolether condensation... 

Boron fluoride/mercuric acetate Self-condensation of enolethers... 

Ketocarboxylic esters condense with AT, as a rule, to give exclusively 7-oxo derivatives (see Scheme 1) an exception is that of a side reaction in a special case (93JHC1325). Esters having instead a 3-acetal or 3-enolether functionality, however, are known to tend to reverse reactivity (e.g., 99EUP947516, 04MI2). 2-Chlorocin-namic acid (15a, Scheme 6) or its ester remarkably also behave so (00CHE1329). 

Chiral (E)-enolethers. A degassed soln. of (5R)-5-cyclohexyl-2-ethenyl-l,3-dioxolan-4-one (2 1 cisjtrans) in THF added to ca. 1 eq. of a suspension of bis(l,5-cycloocta-diene)nickel(0) in the same solvent under N2, stirred until the complex dissolved (10 min), after 3h the resulting rust-coloured precipitate collected, suspended in methylene chloride, treated with MejSiCl, and stirred for 30 min intermediate 7c-allylnickel complex (Y 78%), in benzene treated with DMF and 5 eqs. 1-iodo-propane, irradiated with a sunlamp (GE 275 W Model RSW) for 2,5 h at 10°, stirred for a further 3 h, diluted with pentane to precipitate nickel halide, and stirred for a further 4 h product (Y 82% E/Z 9 1). Subsequent treatment with acetals afforded 2-p-alkoxy-l,3-dioxolan-4-ones with asym. induction, thereby providing an alternative to asym. aldol condensation. F.e. inch reaction with ar. and a,P-ethylene-bromides s. D.J. Krysan, P.B. Mackenzie, J. Am. Chem. Soc. 110, 6273 (1988). 

Orthoesters, like acetals and ketals, condense easily with enolethers in the presence of acid catalysts.— E Propenyl ethyl ether added during 1 hr. with stirring at 30° to ethyl orthoformate containing a little FeClg, stirring continued 1.5 hrs. at 45° l,l,3,3-tetraethoxy-2-methylpropane. Y 70%. F. e. s. I. N. Nazarov, S. M. Makin, and B. K. Kruptsov, 29, 3683 (1959) G. A. 54, 19462d. 

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