Ring-closing metathesis is not limited to the synthesis of carbocycles. Heterocycles containing a carbon-carbon double bond can also be prepared via RCM. Although nitrogen- and oxygen-containing rings are the most common products, heterocycles containing phosphorus, silicon, boron, sulfur, and other elements have also been prepared. It remains important to consider the substitution pattern of the alkene and the activity and functional-group compatibility of the catalyst.
Only the unsubstituted bonds are ring-opened (it is very difficult to metathesize or ROMP tri- and tetrasubstituted olefins).The polymers produced in the ROMP reaction typically have a very narrow range of molecular weights, something that is very difficult to achieve by standard polymerization methods such as free radical polymerization.
Ring Closing Metathesis (RCM) ..
A review. The olefin metathesis reaction is an elegant chem. transformation that entails the metal-carbene-catalyzed cleavage and reassembly of carbon-carbon double bonds. Although simple at first glance, this reaction can be applied in an enormous variety of synthetically useful permutations, such as ring closing metathesis (RCM), cross metathesis (CM), acyclic diene metathesis polymn. (ADMET), and ring-opening metathesis polymn. (ROMP). For this reason, olefin metathesis has become a valuable tool for the prepn. of mols. in org., inorg., biochem., medicinal, polymer, and materials chem. This chapter is concerned specifically with olefin metathesis reactions catalyzed by ruthenium-carbene complexes, mainly because of their great success during recent years. We begin with an overview of these catalysts, and then focus on mechanistic considerations that are important for understanding the reactivity profiles of various catalyst derivs. The second part of the chapter deals with applications of ruthenium-catalyzed olefin metathesis, esp. RCM, CM, and combination processes in org. synthesis. [on SciFinder(R)]
Ring-opening Metathesis Polymerization
When selecting a catalyst for RCM, it is important to consider both the reactivity of the catalyst itself and the structures of the substrate and product. The rate of olefin metathesis is strongly affected by the substitution pattern of the alkene(s), with more substituted alkenes reacting more slowly. Steric hindrance near the reacting alkenes may have an effect similar to alkene substitution.
The facile preparation of alkenyl metathesis synthons
1 Olefin Metathesis Reactions: From a Historical Account.A General Model for Selectivity in Olefin Cross Metathesis Arnab K homodimers toward secondary metathesis reactions.
The facile preparation of alkenyl metathesis synthons Travis W
The vast majority of olefin metathesis reactions are catalyzed by complexes of either molybdenum (Schrock type) or ruthenium (Grubbs type). Molybdenum catalyst 1 was developed before the Grubbs-type catalysts and is highly active, but sensitivity of this catalyst to air and water limits its applicability. Ruthenium catalysts 2 and 3 are less active and cannot be recycled, but exhibit better functional-group tolerance than the rather indiscriminate catalyst 1.
Name Reactions - Organic Chemistry Portal
As in the synthesis of carbocycles, some level of conformational bias in the substrate is important in the synthesis of medium and large heterocycles. For example, bicyclic carbamates containing an eight-membered ring are efficiently synthesized by ring-closing metathesis (Eq. 13). Synthesis of nitrogen-containing rings containing more than nine atoms tends to be problematic.