2-Oxazoline-5-ones ring opening reactions

Saturated 5(4ii)-Oxazolones (2-Oxazolin-5-ones) 7.3.2.5. Other Ring-Opening Reactions... 

Dipolar cycloaddition of 1,1-dimethoxyethene to the mesoionic pyrido[2,l-6][l,3]oxazoline 59 gave the adduct 60.The similar reaction with 61 afforded quinazolin-4-one (62). When 1-dimethylamino-l-methoxyeth-ylene was applied in the latter reaction, a mixture of quinolizin-4-one (63) and the ring-opened product 64 was obtained (88CB951). 

The photochemistry of more complex and highly substituted alkenic partners has been studied. In 1978, Hartmann and coworkers reported the photocycloaddition of 4-oxazolin-2-one with acetone, used as a photosensitizer in the reaction of 4-oxazolin-2-one with alkenyl and alkynyl partners, to form oxe-tane (44). Recently, Scharf has described the photochemistry of 3-acetyl-2,3-dihydio-2,2-dimcthyloxa-zole (45). Irradiation of (45) in the presence of acetophenone produced the oxetane (46) with the phenyl group endo (17%), in addition to 21% of a ring-opened derivative. The stereoselectivity is in agreement with the high exo carboxyl selectivity observed in the photocycloaddition of methyl phe-nylglyoxylate with 2,2-dimethyl-1,3-dioxole to produce oxetane (47). 

Hoefle, G., Prox, A., Stegiich, W. Mechanism of the Dakin-West reaction. III. Ring opening of 4-acyl-2-oxazolin-5-ones by carboxylic acids. Chem. Ber. 1972,105,1718-1725. 

Oxazolin-5-ones (azlactones, 1) in general undergo ring-opening addition reactions with a variety of nucleophiles including water, alcohols,... 

Not only acylimino acids (VI. B.) but also 2-alkylidene- and 2-aryli-dene-A -oxazolin-5-ones (55) (pseudooxazolones) add nucleophiles. Simultaneous ring opening is usually observed 195, 237, 238, 239, 397) yielding the corresponding amino acid derivatives. Reaction with ammonia or amines resp. alcohols yields a,a-diamino carboxylic acid esters (56) or a-alkoxy-a-acylaminocarboxylic acid esters (58) respectively. Mercaptans add so rapidly that mercaptooxazolinones (57) can be isolated and then opened with other nucleophiles. 

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