Methyl 2-diazo-3-oxobutyrate, copper

From the copper-catalyzed reaction of methyl 2-diazo-3-oxobutyrate 57 a with Z-3-methoxystyrene, dihydrofuran 59 (formed with retention of olefin configuration) and butadienol 60 result130). Such an acyclic by-product also occurs when benzofuran is the cycloaddition partner. In that case, however, regioisomers 61 and 62, arising from the connection of the former diazo carbon with either the 2- or 3-position of the heterocycle, are obtained similarly, two isomeric dihydrofurans 63 and 64 are formed under Cu(hfacac)2 catalysis130). 

The copper-catalyzed decomposition of methyl 2-diazo-3-oxobutyrate 57 a in the presence of aldehydes gives ready excess to l,3-dioxole-4-carboxylates 275). Copper(II)... 

---