Coupling of Epoxides and Lactones by Cationic Indium Catalysts To Form Functionalized Spiro-Orthoesters

We prepared a cationic indium catalyst for the conversion of epoxides and lactones into spiro-orthoesters (SOEs), a family of expanding monomers. The cationic indium alkyl complexes [(NNiO)In(CH2SiMe3)(S)][B{3,5-(CF3)(2)C6H3}(4)] (2Solv; H(NNiO)=2,4-dicumyl-6-({[2-(dimethylamino)cyclohexyl]imino}methyl)phenol, S=OEt2 or THF) were synthesized and fully characterized. The reaction of E-caprolactone with 1,2-epoxy-7-octene resulted in the formation of 2-(hex-5-en-1-yl)-1,4,6-trioxaspiro[4.6]undecane (SOE1) with full conversion of both components. We extended the substrate scope to five- and six-membered lactones as well as to a number of functionalized epoxides. The reactivity of the SOEs was explored.