The Synthesis of Phenols and Quinones viaFischer Carbene Complexes

Abstract

Fischer carbene complexes can be broadly defined as those transition‐metal carbene complexes that have a low oxidation state, have an electrophilic carbene carbon , and usually have a heteroatom‐stabilizing substituent on the carbene carbon. Fischer complexes were the first examples of any type of transition metal carbene complexes to be reported. The reaction of Fischer carbene complexes with alkynes is facile, occurring just above ambient temperature, and resulting in the assembly of a benzene ring from the three carbons of the alpha, beta‐unsaturated carbine complex, the two carbons of the alkyne, and the carbon of a carbon monoxide ligand. The synthetic value of this reaction stems from its broad scope, the generally high yields for the process, and the fact that that the products can function as intermediates for the synthesis of a variety of aromatic compounds including para ‐quinones. It is the most synthetically valuable of the large number of Fischer carbene complexes that have been developed for applications in synthetic organic chemistry. This chapter is the first comprehensive review that is limited to the synthesis of phenols and quinones from the reactions of Fischer carbene complexes with alkynes.

Simultaneous Synthesis of Both Rings of Chromenes via a Benzannulation/o-Quinone Methide Formation/Electrocyclization Cascade

“…It should be noted that alkoxyenynes with an internal alkyne function (R 4 ≠ H) gave a single regioisomer of the chromene, specifically, that in which the R 4 substituent is ortho to the methoxy group in complex 5 in Scheme 2. 20 Most of the cases examined involved chromenes in which the sp 3 ethereal carbon of the chromene bears two substituents but we were particularly pleased to note that chromenes with either one ( 26 ) or no substituents ( 24 ) could also be generated. The concern was that alkoxyenynes with either one or both of the substituents R 7 and R 8 as hydrogen would fail since the cation 19 would be less stable.…”

“…This type of five-membered ring cyclized product is perhaps the most common of the many side-products that have been observed in the benzannulation reaction. 20 There is a tendency to see increased amounts of five-membered ring products with increased steric bulk of the two acetylene substituents. Mechanistically, this reaction should occur by initial insertion of the alkyne function of 55 into the metal-carbene bond in carbene complex 53 to give the vinyl carbene complexed intermediate 58 .…”

From supramolecular chemistry to the nucleosome: studies in biomolecular recognition

“…Research in the group spanned organometallic methodology, asymmetric catalysis, total synthesis, and mechanistic studies. I opted for the latter and spent my Ph.D. studying the mechanism of the Wulff–Dötz reaction [1], while at the same time gaining a broad background in methodology and synthesis (Fig. 2).…”

The [5+5] route to the phenanthrene skeleton

“…2 , Scheme 2) and simple carbene complexes ( e.g. 3 ) as surrogates for the coupling of simple alkynes with either α,β-unsaturated chromium carbene complexes 12 or cyclopropylcarbene complexes 13 in various cycloaddition reactions. 14 While looking intensely at this synthetic scheme for conjugated dienyne preparation a novel idea emerged.…”