Grignard reagents, reaction with vinyl ethers

Vinylic ethers. Vermeer et al. have extended the conversion of methoxyallene to 1-alkynes by reaction with Grignard reagents catalyzed by copper(I) halides (6, 146) to a synthesis of vinylic ethers, formulated in equation (11). The ethers... 

Methoxyallene has previously been used to prepare acetylenes via its reaction with Grignard reagents, in the presence of copper(i) halides.The use of preformed dialkylcuprates, however, gave the vinyl ethers instead. The E Z ratio varied with the substituent but it is difficult to explain why the difference is observed.Methoxyallene has also been converted into its vinyl anion and used in the synthesis of dihydrofurans and furans in an analogous way to ordinary vinyl ethers.Similarly allenic cuprates have been prepared and used in the synthesis of allenes and allenic pheromonessome examples are outlined in Scheme 58. The addition of lithium dimethylcuprate to allene phosphine oxides and allenic ketones was interpreted in terms of a 1,2- rather than a 1,4-addition process, in contrast to a/3-unsaturated... 

Electrophilic hydroxylationReaction of this peroxide (1) with Grignard reagents affords the corresponding silyloxy derivatives in 70-90% yield. The reaction with vinyl Grignard reagents results in silyl enol ethers or a-silyloxy ketones. 

Introduction of an alkyl, vinyl- or aryl moiety into the 1-position of a cyclopropylamine was realized by the reaction of l-(l-trimethylsiloxycyclopropyl)piperidine with Grignard reagents to give product 1. ° Addition of the silyl ether to a tetrahydrofuran solution of the Grignard reagent, followed by workup with 10% sodium dihydrogen phosphate solution gave the best results. 

Anodic oxidation of Grignard reagents (5) in the presence of styrene (30), butadiene (36) or vinyl ethyl ether (37) was investigated by Schafer and Kuntzel as an interesting (for preparative use) extension of other anodic reactions with olefins. The electrolysis was carried out at constant current density at Pt, Cu or graphite electrodes. It was found that the products obtained depend on the electrode material, as is seen from the data presented in Table 9. 

THF if CuBr is present.1393 The reaction takes place either with or without allylic rearrangement.1394 Propargylic ethers give allenes.1395 Vinylic ethers can also be cleaved by Grignard reagents in the presence of a catalyst, in this case, a nickel complex.1396 Silyl enol ethers R2G=CROSiMe3 behave similarly.1397... 

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