Organic Synthesis Of N-Heterocyclic Compounds Via 1-Alkynyl Fischer Carbene Complexes

Novel N-heterocyclic structures via 1-alkynyl Fischer carbene complexes were constructed. Efficient demetalation methods of Fischer carbene complexes to obtain nitrogen-containing heterocyclic compounds had been developed.Reactions of substituted pyrazolinones with 1-alkynyl Fischer carbene complexes (OC)5M=C(OEt)C≡CPh (M = Cr, W) afforded a series of bicyclic N-heterocyclic Fischer carbene complexes. The effect of substituents of pyrazolinones was studied. Suitable oxidants such as pyridine-N-oxide (PNO) and m-chloroperoxybenzoic acid (m-CPBA) were found to oxidatively demetalate the newly formed complexes, forming N-heterocyclic organic products including strongly fluorescent mixed bimanes.Demetalation of Fischer carbene complexes was systematically investigated using oxidizing and reducing agents. Oxidative demetalation of 2-alkoxy Fischer mono- and biscarbene complexes was efficiently carried out with pyridine-N-oxide (PNO). Fischer alkoxy biscarbene complexes realized stepwise oxidative demetalation under controlled condition, resulting in ester-monocarbene complexes and diester products, respectively. Sulfuration and selenylation of Fischer biscarbene complexes were achieved by means of in-situ generated SCO and SeCO, efficiently affording thio- and selenocarboxylates. Demetalation of Fischer monocarbene complexes was also investigated with the same method.N-Heterocyclic Fischer biscarbene complexes were synthesized from the reactions of O-alkyl lactims with 1-alkynyl Fischer carbene complexes. Chemoselective oxidation of the biscarbene complexes was stepwisely carried out with pyridine-N-oxide (PNO) to generate partially and completely demetalated products. SiO₂-promoted rearrangement of a chromium biscarbene complex and its thermal annelation were explored. The reaction mechanisms were discussed and the possible reaction pathways were proposed.