Amino Acid-derived Oxazolidinone and Related Auxiliaries

1 Amino Acid-derived Oxazolidinone and Related Auxiliaries 

These complications svere alleviated svhen Evans demonstrated that titanium enolates could be directly generated in dichloromethane svith amine 

To demonstrate the full utility of the (—)-sparteine-mediated enolization, they also showed that oxazolidinone chiral auxiliaries could be reacted with either 1.1 equiv. TiCl4 and 2.5 equiv. (—)-sparteine or 1.05 equiv. TiCl4, 1.0 equiv. (—)-sparteine, and 1.0 equiv. N-methylpyrrolidinone to yield product 94. 

Thiazolidinethione-derived chiral auxiliaries have similar reactivity and selectivity, as shown in Table 2.15. Because of the increased nucleophilicity of the thiazolidinethione ring, chelation-controlled reaction through transition state 85 enabled preferential formation of the non-Evans syn product 101. One equivalent of i-Pr2NEt, TMEDA, or (—)-sparteine and 1 equiv. TiCl4 provided 101 diastereoselectively. Interestingly, when the reaction was performed with 2 equiv. of TMEDA or (—)-sparteine, Evans syn aldol adduct 100 was obtained diastereoselectively. These aldol products can be converted to a variety of other functionality under mild conditions. Other oxazolidinethiones and thiazolidinethiones have resulted in comparable diastereoselectivity and yields. 

Similar reactions utilizing oxazolidineselone chiral auxiliaries were developed by Silks and coworkers [39]. They demonstrated good to excellent 

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