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In polymer chemistry, ring-opening polymerization (ROP) is a form of chain-growth polymerization in which the terminus of a polymer chain attacks cyclic monomers to form a longer polymer (see figure). The reactive center can be radical, anionic or cationic. Ring-opening of cyclic monomers is often driven by the relief of bond-angle strain.
The mechanism of homogeneous ring-opening metathesis polymerization is well-studied. It is similar to any olefin metathesis reaction. Initiation occurs by forming an open coordination site on the catalyst. Propagation happens via a metallacycle intermediate formed after a 2+2 cycloaddition. When using a G3 catalyst, 2+2 cycloaddition is the ...
A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring(s). [1] Heterocyclic organic chemistry is the branch of organic chemistry dealing with the synthesis, properties, and applications of organic heterocycles .
Ring A is synthesized from L-proline through the nonribosomal peptide synthase (NRPS) pathway (figure 2), wherein the pyrrolidine ring of proline is oxidized twice through FAD + to yield pyrrole ring A. Ring A is then expanded via the polyketide synthase pathway to incorporate L-serine into ring B (figure 3). Ring A fragment is transferred from ...
Nicotine is a molecule containing a pyrrolidine ring attached to a ring of pyridine (other heterocyclic amine). Nicotine belongs to a group of compounds known as alkaloids, which are naturally occurring organic compounds with nitrogen in them. Pyrrole is another compound made up of molecules with a five-membered heterocyclic ring. These ...
An example of a [1,7]-electrocyclization of a diphenylethenyl-substituted azomethine ylide is shown below. This conrotatory ring-closing is followed by a suprafacial [1,5]-hydride shift, which affords the rearomatized product. The sterics and geometry of the reacting phenyl ring play a major role in the success of the reaction. [20]
The pyrrolidine ring structure is present in numerous natural alkaloids i.a. nicotine and hygrine. It is found in many drugs such as procyclidine and bepridil. It also forms the basis for the racetam compounds (e.g. piracetam, aniracetam). The amino acids proline and hydroxyproline are, in a structural sense, derivatives of pyrrolidine.
In the ring closing metathesis step, a ruthenium indenylidene complex was used as the precatalyst to afford the desired 7-member ring in 87% yield. [55] In 2002, Stephen F. Martin and others reported the 24-step synthesis of manzamine A with two ring-closing metathesis steps to access the polycyclic alkaloid. [56]