Nicholas-type reaction

Finally, a Nicholas-type reaction is presumably responsible for an unexpected result reported by Alcaide. During their work devoted to the application of the PKR in the field of -lactams and azetidines they reacted complexed azetidine 91 with TMANO, isolating a mixture of the expected PK product 92 and by-product 93. The formation of 93 is believed to be a consequence of the ionization of the propargylic C - N bond at the cobalt-acycle step. The crowded metallacycle formed after the insertion of the olefin (93), would prompt the cleavage of the C - N bond, forming an ionic species (94) that would trap a hydride, possibly from a cobalt hydride giving 95, which then would follow the usual pathway towards the cyclopen-tenone (Scheme 27) [124],... 

Kerr and coworkers have also successfully reported the use of cobalt hexacarbonyl cyclopropanes in [3-1-2] cycloadditions with nitrones via a purported Nicholas-type reaction in the presence of scandium triflate (Sc(OTf)3) to afford a variety of oxazines in high yields (Scheme 10.9) [11]. 

Years earlier, Nicholas and Ladoulis had found another example of reactions catalyzed by Fe2(CO)9 127. They had shown that Fe2(CO)9 127 can be used as a catalyst for allylic alkylation of allylic acetates 129 by various malonate nucleophiles [109]. Although the regioselectivites were only moderately temperature-, solvent-, and substrate-dependent, further investigations concerned with the reaction mechanism and the catalytic species were undertaken [110]. Comparing stoichiometric reactions of cationic (ri -allyl)Fe(CO)4 and neutral (rj -crotyl ace-tate)Fe(CO)4 with different types of sodium malonates and the results of the Fe2(CO)9 127-catalyzed allylation they could show that these complexes are likely no reaction intermediates, because regioselectivites between stoichiometric and catalytic reactions differed. Examining the interaction of sodium dimethylmalonate 75 and Fe2(CO)9 127 they found some evidence for the involvement of a coordinated malonate species in the catalytic reactions. With an excess of malonate they... 

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