Mc. Bagley et al., SYNTHESIS OF FUNCTIONALIZED OXAZOLES AND BIS-OXAZOLES, Journal of the Chemical Society. Perkin transactions. I, (3), 1998, pp. 591-600
A new method for the synthesis of oxazoles, and in particular chiral n
on-racemic oxazoles derived from amino acids, has been developed. Thus
, rhodium(II) catalysed reaction of diazocarbonyl compounds 6 and 11 i
n the presence of amides 8 and 10 results in regioselective insertion
of the carbenoid into the amide N-H bond with formation of the beta-ca
rbonyl amides 9 and 12. Cyclodehydration of amides 9 and 12 using trip
henylphosphine-iodine-triethylamine gives functionalised oxazoles 7 an
d 13. The oxazoles 13e and 13f were converted into the bis-oxazoles 17
a and 17b by a second rhodium(II) catalysed regioselective N-H inserti
on reaction on the amides 15, followed by cyclodehydration.