Nine biotinylated Grubbs–Hoveyda and Grubbs-type metathesis catalysts were synthesized and evaluated in ring closing metathesis reactions of N-tosyl diallylamine and 5-hydroxy-2-vinylphenyl acrylate. Their catalytic activity in organic- and aqueous solvents was compared with the second generation Grubbs–Hoveyda catalyst. The position of the biotin-moiety on the N-heterocyclic carbene was found to critically influence the catalytic activity of the corresponding ruthenium-based catalysts.
Although initial examples of ring-closing metathesis used poorly defined metal catalysts, subsequent development of Schrock-type molybdenum catalysts such as 1 and Grubbs-type ruthenium catalysts such as 2 - 6 greatly expanded the scope and utility of RCM (Eq. 2). In general, molybdenum catalysts display high activity but are unstable toward air or water; ruthenium catalysts are less active but exhibit good selectivity and functional-group compatibility. RCM has been employed extensively in organic synthesis to establish both saturated and unsaturated rings; the reaction can be used to form carbocycles or heterocycles.
Olefin metathesis – ring-closing reaction – Beilstein TV
Four general classes of reactions have emerged: cross metathesis, an intermolecular reaction of two alkenes; ring-opening metathesis polymerization (romp in which a cyclic alkene opens to form a polyolefin; ring-opening metathesis (ROM the opening of a cyclic alkene to form a diene; and ring-closing metathesis.
Mechanism of Ring Closing Metathesis
Unsaturated lactams are a biochemically important class of heterocycles that can be prepared via ring-closing metathesis. Catalyst 1 is effective in the preparation of five- or six-membered lactams, but crotonamides must be used as unsubstituted α,β-unsaturated amides coordinate to molybdenum, preventing reaction (Eq. 16).
Ring-closing metathesis in peptides - ScienceDirect
Because of the synthetic importance of the alkene functional group, a variety of olefination methods were developed prior to the advent of olefin metathesis. While some of these have intramolecular, ring-closing variants, others have not been applied generally for the synthesis of cyclic alkenes. Cross-coupling reactions of alkenyl halides or alkenyl nucleophiles, which establish carbon-carbon single bonds adjacent to C-C double bonds, have also emerged as complimentary alternatives to olefination reactions.
Dimer ring-closing metathesis (PDF Download Available)
Olefin metathesis involves the exchange of two alkylidene groups to generate two new olefins from one or more starting alkenes. Cleavage of the carbon-carbon double bond is accompanied by the formation of two new carbon-carbon double bonds. This reaction was first observed in 1931, investigated by Du Pont and other manufacturers in the 1950's, and finally defined by Calderon in 1967. Partly due to its relevance to petrochemical industry, olefin metathesis reactions have been investigated extensively. Four general classes of reactions have emerged: cross metathesis, an intermolecular reaction of two alkenes; ring-opening metathesis polymerization (ROMP), in which a cyclic alkene opens to form a polyolefin; ring-opening metathesis (ROM), the opening of a cyclic alkene to form a diene; and ring-closing metathesis (RCM), in which reaction of a diene affords a cyclic alkene and a small olefinic byproduct. RCM is the focus of this article (Eq. 1).
Synthesis of Lactams by Metathesis Reactions | …
Ring-closing metathesis is a variant of the olefin metathesis reaction in which alkylidene moieties are exchanged to form a ring. The most common catalysts for this reaction are complexes of molybdenum or ruthenium.