Synthesis Of Dihydrofurans Via The Reaction Of1,3-Disubstituted Benzotriazolium Ylide With3-Benzylidenepentane-2,4-Dione Or2,6-Dibenzylidenecyclohexanone

It is reported that dihydrofurans can be effectively synthesized by the reaction of pyridine ylides or1,4-Diazabicyclo[2.2.2]octane (DABCO) ylides with3-benzylidenepentane-2,4-diones or ethyl2-benzylidene-3-oxobutanoates, etc. all these ylides are generally stabilized by electron withdrawing group such as carbonyl or cyanogroup, etc. In this paper, a new approach for the synthesis of the dihydrofurans via the reaction of1,3-disubstituted benzotriazolium ylides with3-benzylidenepentane-2,4-diones or2,6-dibenzylidenecyclohexanones is reported.It is found that dihydrofurans can be easily prepared from the reactions of1,3-disubstituted benzotriazolium ylides and3-benzylidenepentane-2,4-diones with tetrahydrofuran as the solvent. The reactions of1-methyl-3-phenacylbenzotriazolium ylide or3-methyl-l-(ethyloxyl carbonyl)benzotriazolium ylide with3-benzylidene-pentane-2,4-diones produce trans dihydrofurans in high yield, but the reactions of3-methyl-l-benzylbenzotriazolium ylide with3-benzylidenepentane-2,4-diones yield the mixture of cis dihydrofuran and trans dihydrofuran.It is also found that the hexahydrobenzofuran derivatives can be synthesized via the reaction of1,3-disubstituted benzotriazolium ylides with2,6-dibenzylidenecyclo-hexanones in tetrahydrofuran. The reactions of1-methyl-3-phenacylbenzotriazolium ylide or3-methyl-l-(ethyloxyl carbonyl)benzotriazolium ylide with2,6-dibenzyli-denecyclohexanones produce trans hexahydrobenzofurans in high yield, but the reactions between3-methyl-1-benzylbenzotriazolium ylide and2,6-dibenzylidene-cyclohexanones yield trans hexahydrobenzofuran along with cis and trans spiro[2.4]octan-4-ones.In conclusion, the dihydrofurans can be prepared from the reactions of 1,3-disubstituted benzotriazolium ylides with3-benzylidenepentane-2,4-diones or2,6-dibenzylidenecyclohexanones. The reaction selectivity mainly depends on the stability of the ylide, and the more stable ylide is favourable for the formation of trans dihydrofurans.