Root Inhibitors in Eucalyptus grandis. 2. Synthesis of the Inhibitors and Origin of the Peroxide Linkage

Abstract

Syntheses are described for the three inhibitors G3 (1-hydroxy- 4,4,8,8,10,10-hexamethyl-2,3-dioxabicyclo[4,4,0]dec-5-ene-7,9-dione), G1 and G2 (the diastereoisomers 4-ethyl-1-hydroxy-4,8,8,10,10-pentamethyl- 2,3-dioxabicyclo[4,4,0]dec-5-ene-7,9-dione). Knoevenagel condensation of syncarpic acid with 2-methylpropanal or 2-methylbutanal respectively is followed by slow spontaneous uptake of atmospheric oxygen and cyclization to give the products named. ��� Isolation of the naturally occurring inhibitors from Eucalyptus grandis in an atmosphere of 18O2 results in no incorporation of isotopic oxygen into the peroxide linkage; this indicates that this structural feature was present in the inhibitors in vivo.