Masked ?-formylethyl synthon, compare preceding entry. The derived Grignard, which, unlike the dioxane analogue, is unstable above room temperature, shows similar attenuated reactivity in comparison with simple alkyl Grignard reagents, reacting with acid chlorides to give -ketoaldehydes without carbinol formation, and with enones to give, at low temperatures, predominantly the 1,4-addition product without the need for Cu catalysis:Tetrahedron Lett., 28, 3217 (1987). The Grignard undergoes coupling reactions (CuBr2 + LiCl catalysis) with allylic halides: Tetrahedron Lett., 4549 (1979); J. Org. Chem., 46, 1504 (1981), allylic acetates: J. Am. Chem. Soc., 104, 2269 (1982), and primary alkyl bromides: J. Org. Chem., 48, 1767 (1983). For a review of 3-carbon homologating reagents, including many examples of Grignard and organocuprate reactions of these molecules, see: Chem. Rev., 84, 409 (1984).
