RESUMO
Calculations and experiments were conducted on ozonolysis of ethyl vinyl ether (EVE) and butyl vinyl ether to identify an unconventional diradical intermediate generated from the O-O bond cleavage of primary ozonide. The diradical can undergo a H atom shifting process that yields keto-hydroperoxide (KHP), the characteristic product that identifies the existence of a diradical intermediate. RRKM-ME calculation, based on the PES at the CCSD(T)/VTZ//M06-2X/6-311++G(2df,2p) level, disclosed branching ratios of â¼0.65% for KHP formation. Using synchrotron-generated vacuum-ultraviolet photoionization mass spectrometry measurements, the formation of KHPs (C4H8O4) in ozonolysis of EVE was confirmed by ion signals of C4H8O4+ (ionization of KHP) and C4H7O2+ (ion fragment from the loss of HO2 from KHP) by comparing their photoionization efficiency spectra with the calculated adiabatic ionization energies and appearance energies.
RESUMO
Donor and donor-donor carbenes are two important kinds of carbenes, which have experienced tremendous growth in the past two decades. This review provides a comprehensive overview of the recent development of donor and donor-donor carbene chemistry. The development of this chemistry offers efficient protocols to construct a wide variety of C-C and C-X bonds in organic synthesis. This review is organized based on the different types of carbene precursors, including diazo compounds, hydrazones, enynones, cycloheptatrienes and cyclopropenes. The typical transformations, the reaction mechanisms, as well as their subsequent applications in the synthesis of complex natural products and bioactive molecules are discussed. Due to the rapidly increasing interest in this area, we believe that this review will provide a timely and comprehensive discussion of recent progress in donor and donor-donor carbene chemistry.
