2-Oxazolidinone 2-oxazolone from

Anodic oxidation of the carbamates 17 and 23 in methanol, followed by reaction with chlorodiphenylphosphine affords the a-diphenylphosphinylcarbamates 20 and 25, from which the readily generated carbanions react with aldehydes to give the 4-phosphinyl-2-oxazolidinones 21 and 26. The removal of the diphenylphosphinyl group by a mild thermal treatment provides a route to the 2(3//)-oxazolones 22 and 27 (Fig. 5.6). ... 

The 3-acyl-2(3F/)-oxazolones function as good dienophiles in cycloaddition reactions with cyclic 2,4-dienes such as cyclopentadienes and anthracenes. Thus, the thermal reaction of 3-acetyl-2(37/)-oxazolone with cyclopentadiene and the hexachloro and hexamethyl derivatives gives endo-cycloadducts exclusively. In particular, the chiral cycloadducts 221 and 223 derived from the diastereoselective Diels-Alder reactions of 3-(2-exo-alkoxy-l-apocamphanecarbonyl)-2(3/7)-oxazo-lones with hexamethylcyclopentadiene and 9,10-dimethylanthracene, respectively, are highly useful as chiral 2-oxazolidinone auxiliaries. The conformationally rigid roofed structures play a crucial role in affording excellent chiral induction (Fig. 5.54). 

TABLE 5.13. SYNTHESIS OF 5,5-DIALKOXY-2-OXAZOLIDINONES FROM 5-ALKOXY-2(3//)-OXAZOLONES"... 

Dehydration of 4-hydroxy-4,5,5-trimethyl-2-oxazolidinone 301 with a catalytic amount of p-toluenesulfonic acid affords the isomeric dimers 303 and 304 in a ratio of 1 2. The former type of dimer, that is, 303 likely results from coupling of the isomeric 2(5//)-oxazolone 302A with 4-methylene-2-oxazolidinone 302B, which are the initially formed dehydration products. On prolonged heating in CH2CI2, the 2(5//)-oxazolone dimer 303, completely isomerizes to the 4-methylene-2-oxazoh-dinone dimer 304 (Fig. 5.77). " ... 

TABEE 5.11 SYNTHESIS OF ALKYL 2-OXAZOLIDINONE-4-CARBOXYLATES FROM 5-ALKOXY-2(3H)-OXAZOLONES, 43... 

The alkylation of enolates from some recently developed 2-oxazolidinone auxiliaries will be briefly discussed. The Diels-Alder reaction of the enantiomerically pure 3-(apocamphane-carbonyl)-2(3//)-oxazolone 13 with anthracene gives, diastereoselectively, a 97 3 ratio of diastereomeric adducts63. Recrystallization followed by removal of the apocamphanecarbonyl auxiliary and acylation gives the diastereomerically pure enantiomer 14 in good yield. Subsequent enolate formation and alkylation gives highly diastereoselective reactions and easily purified products due to the fact that the major product is readily crystallized. Thus alkylation... 

D. 3-Aaetyls 3H)-oxazolone. The crude mixture of 3-acetyl 4- and 5-chloro-2-oxazolidinone from Step C is placed in a 2-L, three-necked flask equipped with a thermometer, sealed mechanical stirrer, and gas discharge tube. The material is heated to 120°C with stirring, and the temperature is then slowly increased to 150 C and held there until the evolution of gas ceases (Note 10). The cooled, black reaction mixture is distilled at 20 mm. The fractions boiling up to 150°C are collected and redistilled through a 50-cm x 3-cm Vigreux column fitted with a variable take-off head. There 1s obtained 140-172 g (55-68%) of product, bp 108-U2°C (24 mm), which solidifies, mp 35-37 C (Note 11). 

Oxazolone itself can be easily obtained from oxazolidinone through electrochemical reduction as described in CHEC-II(1996). A similar sequence was utilized in the synthesis of indole-substituted 2(3//)-oxazolone 244 (Scheme 71) <1997CPB733>. Electrochemical oxidation of 2-oxazolidinone in methanol gave a 4-methoxy oxazolidinone 241, which reacted with an organomagnesium indole reagent 242 in the presence of BF3-Et20, followed by... 

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