Preparation, metallation and alkylation of allenyl ethers

Abstract

AbstractPropargyl ethers HCCCH2OR [R = alkyl or‐CH(CH8)(OC2H5)] have been isomerized with good yields into the corresponding allenyl ethers CH2CCHOR by warming with potassium tert.‐butoxide at 70°.These allenyl ethers can be metallated with butyllithium in ether or alkali amides in liquid ammonia. In ether, subsequent alkylation with alkyl halides R′Hal affords α‐substituted allenyl ethers CH2CC(R′)OR. Alkylation in liquid ammonia produces a mixture of this same compound and the γ‐substituted product R′CHCCHOR. In both cases reasonable yields are obtained. Sodamide and potassium amide quickly convert allenyl ethers CH2CCHOR into metallated propargyl ethers MCC‐CH2OR (M = Na or K). If alkylation is not performed almost simultaneously with the metallation with sodamide or potassium amide, the only alkylation product obtained is R′CCCH2OR.