Hydromagnesiation acetylenes

Since then, hydromagnesiation of other unsaturated hydrocarbons such as conjugated dienes and acetylenes has been investigated intensively.5 6 Hydromagnesiation of 2-alkyl substituted 1,3-butadienes has been shown to proceed... 

The hydromagnesiation of acetylenes, catalysed by titano- and zirconocenes is well known. A regioselective reaction occurs only if one of the substituents on the triple bond is silicon or an aryl group. Studies on its mechanism were reported by Sato.2 7 Cai has applied this reaction for the synthesis of a number of polysubstituted alkenes (Scheme p).28-28 -2 ... 

COOPER-FINKBEINER Hydromagnesiation Ti catalyzed formation of Grignard reagents from olefins or acetylenes. 

Conlrarily, Grignard reagent-mediated hydromagnesiation of acetylenes in the presence of... 

COOPER - FINKBEINER Hydromagnesiation Ti catalyzed reaction ot Grignard reagents with olefins or acetylenes... 

Table 3.5. Hydromagnesiation of dialkylacety Icncs and aromatic acetylenes with Grignard reagent.s...

The accepted mechanism of the aforementioned liydromagnesiation of acetylenes in the presence of CpiTiCh can be drawn as in Scheme 3.12, which resembles that for hydromagnesiation of oletins in the presence of TiCLt (see Scheme 3.5 where the catalytically active species is CljTiH 5 ). 

Some discrete observations relevant to the mechanistic hypothesis have been reported. It has been shown that an equilibrium is attained between a starting acetylene and the alkenyl Grignard reagent produced by the hydromagnesiation, provided that the acetylene is a silylated one (eq. 3.58) [102]. Thus, the addition of a different acetylene to the silylalkenyl Grignard reagent, preformed from the... 

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