Mode of Epoxide Ring Opening

The polymerisation of racemic propylene oxide with coordination catalysts leads to a polymer that can be fractionated into crystalline and amorphous polypropylene oxide)s  

One can note, in this connection, that styrene oxide undergoes polymerisation in the presence of aluminium isopropoxide which involves a selective cleavage of the Ca-0[CH(Ph)—O] bond [47]. On the other hand, polymerisation of styrene oxide with the diethylzinc-water catalyst was found to proceed via 0,8-0(0142—0) bond scission [48], 

It has been found that the polymerisation of propylene oxide with catalysts characterised by an isolated metal atom surrounded by a porphyrin [49,50], Schiffs base [40,51] or calix[4]arene [41] moiety also proceeded by Cp—O bond cleavage. 

The polymerisation of epoxides with coordination catalysts has been established to proceed with the inversion of the configuration at the carbon atom of the epoxide ring where cleaved  

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With good nucleophiles, under relatively mild conditions, 2,3-epoxy alcohols will undergo epoxide ring opening at C-2 or C-3. In simple cases, nucleophilic attack at C-3 is the preferred mode of reaction. However, as the steric congestion at C-3 is increased, or if substituents play a significant electronic role, attack at C-2 can predominate.86... 

The previous example illustrates a frequently encountered epoxide ring-opening mode, lamely the (3-elimination. Indeed, this reaction is of general importance, and can be induced by lase- and acid-catalyzed routes, as well as homolytic sequences. For example, Singh and co-.vorkers <97T1855> have found that the lithium diethylamide (LDEA)-induced rearrangement of... 

An interesting alcoholysis of epoxides has been reported by Masaki and coworkers <96BCSJ195>, who examined the behavior of epoxides in the presence of a catalytic amount of the Tt-acid tetracyanoethylene (TCNE, 85) in alcoholic media. Ring-opening is very facile under these conditions, typically proceeding via normal C-2 attack, as exemplified by styrene oxide (86). Certain epoxy ethers (e.g., 89) undergo C-1 attack due to anchimeric assistance. Analysis of the reaction mixtures revealed the presence of captodative ethylenes (e.g., 85) formed in situ, whieh were shown to be aetive in eatalyzing the reaction. The proposed mode of catalysis is represented by the intermediate 87. The affinity of these captodative olefins for... 

Using these patterns, it was possible to speculate on the preferred epoxidation sites and possible ring opening modes, which could induce similar charge delocalization paths. In relation to metabolic epoxidation and subsequent DNA adduct formation, these patterns pointed to the possible importance of K-region and M-region epoxides for some of the methano-PAHs. 

Polymerization using epoxides as monomers includes the ring opening of epoxides via C-O bond cleavage. Thus, a mode of G-O bond cleavage (Sn2 or SnI) and selectivity, that is, which C-O bond is cleaved, coupled with the symmetry of epoxides (symmetrical or unsymmetrical), cause regio- and stereochemical issues to be controlled in the epoxide polymerization. 

Three recent publications have dealt with the photochemical reactivity of epoxynaphthoquinone derivatives [e.g., (275)]. In contrast with the reactions of (269), one of the principal reaction modes involved ring-opening of the epoxide to afford the ylide (276), which can be trapped by several reagents. 

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