Oxazolidines ring-opening reaction

Amino alcohols. By decomposition of allylic azidoformates to produce bicyclic oxazolidinone substrates for ring opening reactions, a stereoselective entry into jyn-1,2-amino alcohols is delineated. Thus, after treatment of the aziridines with organocopper species, trani-4,5-disubstituted oxazolidin-2-ones (14 examples, 55-91%) are obtained. 

Oxazolines can be obtained by the Lewis acid catalyzed epoxide ring opening of glycidic esters or amides (e.g., 118) with acetonitrile . Oxazolidines are available from the palladium-catalyzed cycloaddition of vinyl epoxides with imines <00H885> or the samarium-promoted reaction of ketimines (e.g., 120) with unfunctionalized... 

The dimethyl ester of adipic acid, rather than adipic acid, was used as a transesterification substrate. Reaction rate studies had shown that the transesterification would be much faster than the esterification reaction. It was considered that the rate of attack on the oxazolidine ring by methanol would be slower than the rate of attack by water and that the ring opening would not be catalysed by the enzyme, whereas the rate of the transesterification would be increased significantly, particularly at the low temperature of the enzymatic esterification. 

Upon warming, these oxazolinyl-stabilized lithiooxiranes undergo an electrocyclic a-ring opening to give a-oxo-2-oxazolines after hydrolysis (Scheme 87). However, all attempts to quench the presumed oxazolidine enolate intermediates through reaction with electrophiles failed. 

Few solid-phase syntheses of oxazoles have been reported (Table 15.17). The most general strategy is the dehydration of a-(acylamino) ketones (Entry 2, Table 15.17) or 2-(acylamino)phenols (Entry 1, Table 15.17). Oxazolidin-2-ones have been prepared by intramolecular nucleophilic cleavage of carbamates from insoluble supports (Entries 5 and 6, Table 15.17). Resin-bound 2-aminoethanols, which are accessible by nucleophilic ring-opening of oxiranes with amines, undergo cyclocondensation with aldehydes to yield oxazolidines [220,221]. These compounds are unstable towards acids, and can be released from the support only under neutral or basic reaction conditions. 

In any event, no such phenomenon can explain the unretarded hydrolysis of 1,3-dioxolanes. The reaction is the exact analogue of the ring-opening of oxazolidines, and so the leaving group cannot become antiperiplanar to an sp3-type lone pair orbital on oxygen. In a detailed study, Fife and Jao (1965)... 

The ring-chain tautomerism of oxazolidines is discussed in Section 4.18.2.5.2. Oxazolidines form unstable salts which are easily hydrolyzed (equation 80) (77RRC1413). IV-Substituted oxazolidines react with enamines in the presence of trifluoroacetic acid to yield 1,4-oxazepines in a ring-opening 1,5-cycloaddition reaction (equation 8,1) (80LA1573). 

Dipolar cycloaddition methodology has also been utilized in a one-pot three-component system to generate oxazolidines 292 <2005T6088>. Reactions between sulfonyl azides and vinyl ethers, for example 289, generated aziridine intermediates 290, which then reacted via ring-opened zwitterionic intermediate 291 with aldehydes to generate the oxazolidines in good yields (Scheme 82). 

Formation of a cation radical of the diene may catalyze Diels-Alder reactions with certain dienophiles thus oxidation of substituted vinylindoles to the cation radical in the presence of a push-pull dienophile may form different heterocyclic compounds by the Diels-Alder reaction, for instance pyrido[l,2i7]indoles from vinylindoles and yS-enamino-esters [33]. Similarly, anodic oxidation in MeCN of certain oxazolidines in presence of vinyl ether leads to derivatives of oxazepines in a catalytic reaction in which the ring-opened radical cation of the oxazolidine adds to the vinyl ether and the radical cation of the resulting oxazepine oxidizes the oxazolidine [34]. 

Cleavage of oxazolidines. A route to a-substituted allyl amines starts from A-acetyl (X-amino acids via the oxazolidinones. The latter compounds are converted to dichloromethylene derivatives by reaction with PhjP-CCl and the final step involves dechlorination and ring opening (and removal of an HCO unit) with Na in refluxing THF. 

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