5 -oxazolones, unsaturated diazomethane

TABLE 7.47. OXAZOLONE SPIROCYCLOPROPANES FROM 1,3-DIPOLAR CYCLOADDITION REACTION OF UNSATURATED 5(4/7)-OXAZOLONES WITH DIAZOMETHANE... 

During the last two decades, the importance of the dipolarophilic nature of unsaturated 5(4/l/)-oxazolones has been widely recognized and studied with a variety of 1,3-dipoles. Among the systems studied, diazoalkanes, particularly diazomethane, are the most frequently used and have opened the way for the synthesis of aminocyclopropanecarboxyhc acid derivatives. 

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>. 

---

See also in sourсe #XX -- [ , , , , , , , , ]

---