Grignard derivatives, acetylenes

When acetylene is passed through a 0.5 to 1 molar solution of C2HjMgBr, kept just below 30 C (compare exp. 13) the solution initially remains clear, but there is a fair chance that the characteristic precipitate of BrMgOCMgBr appears (clearly different from the coarser suspension which is sometimes formed when solutions of HOCMgBr are cooled). If acetylene is introduced at 50 C into a-solution of C2HjMgBr, the suspension of the di-Grignard derivative is formed immediately. 

The trimethylsilylation of the di-Grignard derivative of acetylene has to be carried out at temperatures that are considerably higher than those necessary for the silylation of ethynyl mono-magnesium bromide. This decreased reactivity may be ascribed to the slight solubility of the intermediate. 

TRISUBSTITUTED ALKENES FROM ADDITION OF GRIGNARD-DERIVED ALKYLCOPPER COMPLEXES TO ACETYLENES,... 

The reaction with cyanogen bromide presumably can also be carried out succesfully with RCsCLi in EtjO-hexane mixtures or with acetylenic Grignard derivatives (at higher temperatures) in Et20 or THF. 

Synthesis of heterocycles. Quilico and co-workers used the reagent for the synthesis of 3-chloroisoxazoles from the Grignard derivatives of terminal acetylenes. 

The classical route to bisilylacetylenes is the reaction of the di-Grignard derivative of acetylene (188) (equation 88)116. Also, the reaction of tetrachloroethene (53) with lithium and Me3SiCl in THF at — 78 °C gives rise to 189 (equation 89)114. Alternatively, the application of methyllithium to halogenated alkanes or alkenes with subsequent employment of bromo- or fluorosilanes affords bis-silylated acetylenes (equation 90)115. 

By means of the CuCl-TMEDA complex as a catalyst one can synthesize 1,4-bis(TMS)-l,3-butadiyne (207) from TMS-acetylene (57a) in the presence of oxygen (equation 98)123. Alternatively, 207 and the corresponding TES-compound (210), respectively, can be formed by the reaction of 16 or the corresponding TES-C1 (209) with the di-Grignard derivative of 1,3-butadiyne (208) (equation 99)124 125. 

Allylic rearrangement has enormously increased the difficulty of determining the structure of many compounds of allylic type, but on the other hand there is a whole series of cases in which it has been put to preparative use. For example, Heilbron and his co-workers15 prepared the dienynediol (1) from crotonaldehyde and the Grignard derivative of acetylene and converted it jnto the isomeric diol (2) by a double allylic rearrangement ... 

Grignard derivatives of acetylenes have also been used for ring-closure reactions, as is illustrated by the preparation of l,6-dioxa-3,8-cyclodecadiyne (12) from bis(bromomagne-sium)acetylene (11) and di(chloromethyl)ether (10) [Eq. (2)] [7],... 

Acetylenic Grignard compounds or the corresponding organoalkali metal derivatives are important intermediates in many syntheses of acetylenic compounds. The various methods for their formation in organic solvents and in liquid ammonia have been discussed extensively and we here give only a brief summary. 

Another method of synthesis was also used. This involved the action of chloroacetaldehyde on the Grignard reagent derived from acetylene in order to obtain the meso divinylacetylene dichlorohydrin, CH2CI—CHOH—C=C—CHOH—CH C1, from which one passed to the corresponding hexynetetrol, CH2OH—CHOH—C=C—CHOH— CHjOH. This, in turn, was reduced to the hexenetetrol, CHjOH— CHOH—CH=CH—CHOH—CH2OH, by means of Bourguel s catalyst,8 a dispersion of colloidal palladium on starch. When the hexenetetrol was hydroxylated by the use of silver chlorate and osmic acid, two hexitols, dulcitol and allitol, were obtained. 

The desired intermediates, a pentadienol or a pentenetriol were unknown at the time, but it occurred to me that their synthesis might be accomplished by the partial reduction of a pentenynol or a pentynetriol, the latter being obtained from the reaction of one molecule of acrolein or acrolein dichloride with the Grignard reagent derived from acetylene. The reactions which have been carried out in accordance with this scheme are shown in the accompanying flow sheet. 

Selenienylalkynylcarbinols were prepared by the addition of Grignard reagents or the sodium salts of acetylenes to 2-formylselenophene and its derivatives. The alcohols were oxidized and the resulting ketones treated with hydrazine and hydroxylamine to give the diheteroaryls 81 and 82.94... 

In the general context of donor/acceptor formulation, the carbonyl derivatives (especially ketones) are utilized as electron acceptors in a wide variety of reactions such as additions with Grignard reagents, alkyl metals, enolates (aldol condensation), hydroxide (Cannizzaro reaction), alkoxides (Meerwein-Pondorff-Verley reduction), thiolates, phenolates, etc. reduction to alcohols with lithium aluminum hydride, sodium borohydride, trialkyltin hydrides, etc. and cyloadditions with electron-rich olefins (Paterno-Buchi reaction), acetylenes, and dienes.46... 

High yields of -substituted allenic primary amines 227 are obtained by the CuBr-Me2S-or NiCh Ph2PCH2CH2CH2PPh2-catalysed reaction of the acetylene derivative 226 with aryl Grignard compounds and subsequent deprotection by flash chromatography219. 

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