Metalated 2-Alkenyl- and 1,2-Alkadienyl 2-Tetrahydropyranyl Ethers : Versatile Building Blocks for Furan Syntheses

Me3CLi metalated LiOCH2C:CCH2OTHP (THP = tetrahydro-2-pyranyl) quant. to LiOCH2CLi:C:CHOTHP which was treated with MeOH, Me(CH2)5I, or PhCH2Cl to give LiOCH2CR:C:CHOTHP [I; R = H, (CH2)5Me, CH2Ph]. Treating I with Me3CLi gave LiOCH2CR:C:CLiOTHP [R = (CH2)5Me] which was alkylated to LiOCH2CR:C:CR1OTHP [II; R = (CH2)5Me, R1 = Me, CH2CH:CHMe]. I and II were hydrolyzed by dil. acid and cyclized to 39-67% furans III [R = (CH2)5Me, R1 = H, Me, CH2CH:CHMe; R = CH2Ph, R1 = H]. In the same way, LiOCHR2C.tplbond.CCH2OTHP [R2 = Ph, CH:CMe2, Me, Pr, (Z)-CMe:CHMe] and LiOCHR3C.tplbond.CCHMeOTHP [R3 = Pr, (CH2)5Me] were converted into 53-81% furans III (R = H, R1 = CH:CMe2, Ph), IV [R = Me, R1 = (CH2)4Me; R = Pr, R1 = Et; R = CMe:CMe2, R1 = Me], and V [R = [(CH2)5Me, R1 = H, R = Pr, R1 = Et, R2 = Me]. [on SciFinder (R)]