SYNTHESIS AND HERBICIDAL ACTIVITY OF -3-BENZYLOXY-5-METHOXY-1,7-DIOXASPIRO[5.5]UNDECANE AND -3-METHOXY-5-BENZYLOXY-1,7-DIOXASPIRO[5.5]UNDECANE

The synthesis of spiroacetals 3-benzyloxy-5-methoxy-1,7-dioazaspiro[5. 5]undecane 3 and 3-methoxy-5-benzyloxy-1,7-dioaxaspiro[5.5]undecane 4, where the substituents on the spiroacetal assembly are in a 1,3-diaxi al orientation, is described. Epoxidation of unsaturated spiroacetal 5 using dimethyldioxirane showed greater preference for the alpha-epoxi de 11 over the beta-epoxide 12. Treatment of the alpha-epoxide 11 with lithium diethylamide in tetrahydrofuran afforded both the allylic alc ohol 7 and the homoallylic alcohol 13 in approximately equal amounts. Use of a nonpolar solvent (hexane) suppressed the isomerization of the allylic alcohol 7 to the homoallylic alcohol 13, affording a 21:1 rat io of 7:13. Coordination of an oxygen lone pair with the electron-defi cient lithium center of the reagent sets up a transition state in whic h abstraction of a syn-proton and opening of the epoxide leads to ster eoselective formation of allylic alcohol 7 with a pseudoaxial hydroxyl group at C-5. The hydroxyl group liberated in the epoxide rearrangeme nt step was then used to direct a second epoxidation to the lower face of the alkene. Thus, treatment of alcohol 7 with m-CPBA buffered with sodium acetate afforded or-syn-epoxy alcohol 9. Subsequent epoxide op ening using lithium aluminum hydride proceeded smoothly, affording syn -3,5-diaxial diol 10 and 4,5-diol 22. Epoxy alcohol 9 was then treated with sodium hydride and methyl iodide or benzyl bromide, affording me thyl ether 23 or benzyl ether 24, respectively. Reduction of methoxy e poxide 23 with lithium aluminum hydride then afforded alcohol 25 toget her with the regioisomeric alcohol 27. Benzyloxy epoxide 24 afforded a lcohols 29 and 31. Finally benzylation of alcohol 25 afforded bis-ethe r 3 whereas methylation of alcohol 29 afforded bis-ether 4. Spiroaceta ls 3 and 4 were screened for herbicidal activity and exhibited signifi cant activity against the weeds Avena fatua, Setaria viridis, Amaranth us retroflexus, and Chenopodium album when applied preemergence. Bis-e thers 3 and 4, which contain alkoxy groups anchored in a 1,3-diaxial o rientation on a spiroacetal ring, represent the first examples of herb icides based on a spiroacetal ring system.