Ring-opening of cyclopentene oxide

Scheme 12.25. Ring-opening of cyclopentene oxide in the presence of 4.

Scheme 5.9 Enantioselective ring-opening of cyclopentene oxide...

Recently, a new method to synthesize aluminum oxide that contains high surface Lewis acidity relative to surface hydroxyls without dehydroxylation at elevated temperatures was reported [3]. It was shown that this oxide, compared with one prepared by a conventional method, contains a much higher density of surface Lewis acid sites relative to hydroxyl groups. Furthermore, these surface Lewis acid sites are catalytically active. The solid catalyzes ring opening of cyclopentene oxide with piperidine to form 2-piperidylcyclopentanol selectively [4]. In this chapter, a description of the preparation method and characterization of the steps in the synthesis will be presented. 

Phenyl-substituted cyclopentadienes 1211 are converted to pyrylium salts 1214 in the presence of silver(l) perchlorate via insertion of an oxygen atom into the cyclopentadiene ring. The reaction proceeds via ring opening of cyclopentene 1212 followed by electrocyclic ring closure and oxidation of the resulting 2,4-dienone 1213 (Scheme 296) <2004JOC1432>. 

The metal catalyzed ring opening of epoxides followed by reaction with CO or COj to form P-lactones and carbonates is a useful reaction that continues to attract attention. In an expansion of previous work, Coates and co-workers have developed an improved catalyst, 99, for the carbonylation of epoxides <05JA11426>. These reaction conditions are compatible with a wide variety of side chains, including those bearing Lewis basic functionality. Interestingly, the cyclopentene oxide 97 was readily converted to the P-lactone 98 in excellent yield. 

A lead(ii) coordination polymer 4, prepared from disodium 1,5-naphtha-lenedisulfonate and 1,10-phenanthroline with lead acetate hydrate (Figure 22.2) has been reported to catalyse the ring opening of epoxides (styrene oxide, cyclohexene oxide, cyclopentene oxide with anilines) with very high yield. ... 

Enantioselective ring opening of epoxides was attained with (salen)Cr(III) complex (191) [68]. Cyclopentene derivatives (190) were converted with Me3SiN3 to azide-alcohols (192) in 80-90% yields up to 98% ee (Scheme 16.56). Kinetic resolution of racemic styrene oxide was performed in 98% ee. This reaction was applied to practical synthesis of enantiopure cyclic 1,2-aminoalcohols by reduction of the azide products by Pt02-catalyzed hydrogenation [69], to synthesis of cyclopentenone derivatives [70] to formal synthesis of bioactive compound Balanol [71], and to solid-phase synthesis of peptides [72]. 

A variety of ie.so-epoxidcs could be selectively ring-opened this way with e.e. s as high as 97% [28], The azides can be converted to 1,2-amino alcohols, which are very desirable synthetic intermediates. Surprisingly, the mechanism of the ARO (asymmetric ring-opening) was more complicated than expected [29], First, it turned out that the chloride ion in Cr-salen was replaced by azide. Secondly, water was needed and HN3 rather than Me3SiN3 was the reactant nucleophile. Thirdly, the reaction rate was found to be second order in catalyst concentration, minus one in epoxide (cyclopentene oxide), and zero order in HN3 [30],... 

Long-chain derivatives of pyrazolyl pyridines coordinated to MoO(02)2 as 35 may efficiently replace the conventional Mo(CO)e in the oxidation of several double-bond typologies with TBHP, in non-polar hydrocarbon solvents . The epoxidation of cyclopentene and 2,3-dimethyl-2-butene led to the corresponding epoxides, notoriously sensitive to ring opening, in 100% and 87% yield respectively, in isoctane, with 1 hour reaction time. Recent advances in the epoxidation of a-pinene and other terpenes using the Mo-TBHP system have been reported. ... 

Sn2 ring opening by attack of a nucleophile on an ethenyl substituent (e.g. Scheme 60) has assumed importance in natural products synthesis (80JCS(P1)2084, cf. 81JA5969). The cyclopentene oxide (63) is a versatile synthon for alkylated, functionalized cyclopentanes (Scheme 61) (81JA2112). 

Epoxides which are fused to alicyclic systems undergo ring opening with azide ion in the usual tram diaxial manner This is demonstrated by the formation of the /ran5-2-azidoalcohols (66) and (67) from cyclohexene oxide and cyclopentene oxide respectively . 

It was shown by Ortiz de Montellano et al. that bicyclo[2.1.0]pentane was oxidized by rat liver microsomes to a 7 1 mixture of e <7o-2-hydroxy-bicyclo[2.1.0]pentane and 3-cyclopenten-l-ol, consistent with a radical ring-opening reaction. Applications of the radical-clock method by Ingold and by Newcomb began to measure the lifetime of the suspected radical cage intermediate. The rate constant for the rearrangement of bicyclo[2.1.0]pent-2-yl radical to 3-cyclopenten-... 

Cyclic /neso-epoxides, such as cyclopentene oxide (64), can be induced to undergo alkylative ring-opening in the presence of trialkylaluminum reagents under catalysis using N-heterocyclic carbenes (62). These unusual catalysts are derived from the deprotonation of imidazolinium salts (61), and serve as phosphine mimics in terms of electron-pair donation behavior to form aluminum complexes of the type 63 <01 OL2229>. 

The ring-opening polymerization of cyclopentene to polypentenamer was first carried out by Eleuterio [57] who used heterogeneous catalysts based on oxides of chromium, molybdenum, tungsten, or uranium [Eq. (12)]. 

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