Homologation of Five-Membered Heterocycles

In sharp contrast to the behavior of epoxides and oxetanes, tetrahydrofuran itself (26a) does not undergo reductive opening by means of lithium metal alone or even in 

E+= Pr CHO, BunCHO, Bu CHO, PhCHO, p-MeOC6H4CHO, Et2CO, MeCOBu, MeCOPh 

Cyclic alkyl aryl ethers lead also to functionalized organolithium compounds by reductive carbon-oxygen bond cleavage in arene-catalyzed lithiation process. Thus, the treatment of 2,3-dihydrobenzofuran (47) with an excess of lithium in the presence of a catalytic amount of DTBB in THF at 0°C gives the dianion (48) which after reaction with different carbonyl compounds and final hydrolysis with water leads to 

R1R2CO = Bu CHO, PhCHO, PhCH2CHO, Ph(CH2)2CHO, furfural, Me2CO, Et2CO, (CH2)5CO, (CH2)7CO, (-)-menthone 

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