Tetronic acids, ring synthesis

Effenberger and coworkers have utilized the tolerance of methyl ketones by the recombinant enzyme to develop an alternative synthesis of tetronic acids and their amino derivatives, as shown in Figure 5.18. Treatment of O-acyl cyanohydrins with lithium disilazide resulted in base-induced ring closure to amino tetronic acid derivatives. Alternatively, the cyanohydrins could be converted to a-hydroxy esters prior to acylation, and the same base-induced cyclization then led to tetronic acid derivatives [89]. 

A [4 + 2 +1] domino cyclization in water involving condensation of 2,2-dihydroxy-indene-l,3-dione (149), tetronic acid 150 and OPD catalyzed by acetic acid has been developed for the synthesis of spiro-substituted benzofurodiaz-epine derivatives 152 and 153 (Scheme 32) in a one-pot manner xmder MW proceeding within few minutes [102]. The authors observed that the outcome of tiie process was dependent on the ratio of reactants as well as on the electronic effects of the substituent in the aromatic ring of the diamine. 

---