Cyclopropanation, unsaturated 5 oxazolone

Sulfur ylides are among the most interesting carbon nucleophiles and their synthetic importance has been recently reviewed.One especially interesting use of these ylides is their application to the synthesis of cyclopropane derivatives using unsaturated oxazolones. For example, stabilized sulfur yhdes react with unsaturated oxazolones 629 via a Michael reaction to give oxazolone spirocyclopropanes 630 as shown in Scheme 7.202 and Table 7.46 (Fig. 7.57), whereas the less stabilized sulfur ylides give ring-opened products 631 as the major compounds (Scheme 7.202). ... 

Since (Z)- and ( )-stereoisomers of unsaturated oxazolones can be obtained using appropriate isomerization procedures, cis and trans isomers of cyclopropane derivatives can be obtained in a stereoselective manner, although special care must be taken with experimental conditions to obtain the best stereoselectivity. Both racemic cis- and fraui-l-amino-2-phenylcyclopropanecarboxylic acid 641 and 644 have been obtained from the corresponding (Z)- or ( )-4-benzylidene-2-phenyl-5(4//)-oxazolone 621 and 642 using diazomethane. Care was taken to affect the... 

Unsaturated 5(4//)-oxazolones have an additional exocylic double bond which has been exploited in various reactions. Chiral oxazolone 120 undergoes diastereoselective reaction with diazomethane to give cyclopropane adduct 121, which can be transformed into various cyclopropylamino acids 122 (Scheme 29) <1996T5881>. 

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