Chemistry of acetylenic ethers. Part 89: The reaction of organolithium compounds with 1‐alkynyl ethers

Abstract

Disubstituted acetylenes C 4 H K = C R are produced in the reaction of I-ethoxy-1-hexyne C4H!,C-COCzHs with organolithium or Grignard compounds RLi or RMgBr. The yields are moderate to satisfactory. Ethoxyethyne HC-COCzHs and phenyllithium CsHsLi afford phenylacetylene HCE CC6H5 (after hydrolysis) in moderate yield.The formation of acetylenes probably proceeds by an addition-elimination mechanism.In a previous paper we presented a new and simple route to l-alkynylamines (ynamines), consisting of conversion of 1 -alkynyl ethers with lithium dialkylamides 1. The intermediary of an adduct was considered likely:This reaction, in which the acetylenic ether acts as a n electrophilir * cdkynylation agent, has been extended to some other organolithium compounds, wz, CH3Li, n-C4HgLi, t-CdH ,Lj, 1-cyclohexenyllithium, a-thienyllithium, and phenyllithium. The expected products were obtained in moderate to good yields (see Table I):Phenylmagnesium bromide, when employed instead of phenyllithium, gave a poor result. A partial isomerization of dibutylacetylene C4HgC= CCJHB into the allene C~H .~C H = C = C H C~H B was observed in the reaction of ethoxyhexyne with an excess of butyllithium.* The usual alkynylation reagents (metal alkynylides) are nucleophilic. P. P.Montijn, E. Harryvan and L. Brundsma, Rec. Trav. Chim. 83, 121 I (1964).

Ynol Ethers: Synthesis and Reactivity

“…The intermolecular carbolithiation of ynol ethers generates an unstable vinyllithium intermediate that spontaneously β-eliminates to produce the corresponding internal alkyne (Scheme 8a). [34] Nevertheless, via an intramolecular cyclisation, the regioselectivity of the carbometallation can be reserved with an anti carbolithiation process, leading to a more stable organolithium species that can be trapped with various electrophiles (Scheme 8b). [35] Normant and Alexakis reported the carbocupration of ynol ethers affording the vinyl ethers with a lack of selectivity when the triple bond was substituted.…”