Maleates from diazoacetates and dilactones from head-to-head dimerisation of alkenyl diazoacetates using Grubbs' 2nd-generation ruthenium carbene catalyst.

Grubbs' 2nd-generation ruthenium carbene catalyst homocouples diazoacetates to maleates and also catalyses head-to-head dimerisation of alkenyl diazoacetates giving dienyl dilactones.