Selective Oxyfunctionalization of (Tricarbonylcyclohexadiene)iron‐Substituted Furans with Singlet Oxygen and Dimethyldioxirane

Abstract

AbstractThe versatility of the tricarbonyliron fragment as protecting group in the oxyfunctionalization of cyclohexadienyl‐substituted furans with singlet oxygen (1O2), dimethyldioxirane (DMD) and m‐chloroperoxybenzoic acid (mCPBA) was investigated. The photooxygenation of the (tricarbonylcyclohexadiene)iron‐substituted furans 1a and 1b in methanol gave, after reduction with triphenylphosphane, the furanone 2a and the enediones 3b as mixture of Z and E isomers in good yields. Precursors to these oxyfunctionalized products were the corresponding furan endoperoxides, which were trapped by methanol. The enedione Z‐3b was also obtained in the dimethyldioxirane oxidation, which was performed in boiling acetone to minimize the oxidative destructin of the tricarbonyliron moiety. In contrast, mCPBA was unsuitable for the oxyfunctionalization of the ligand sphere of such tricarbonyliron complexes due to the liberation of the organic ligand. While the decomplexation of the furanone 2a with cerium (IV) ammoniumnitrate (CAN) led selectively to the functionalized cyclohexadiene 4a, photooxygenation of the free furan 6a resulted in a complex mixture of oxidized compounds. Thus, protection of the 1,3‐cyclohexadiene moiety by tricarbonyliron complexation, oxidation (1O2, DMD) and decomplexation (CAN) offers a convenient and useful sequence for the regioselective oxyfunctionalization of such complex furans.