Grignard reagents, reaction with epoxides

In 1974, Vermeer et al. described formation of allenic alcohols 61 by the reaction of alkynyl epoxides 60 with Grignard reagents in the presence of 10mol% of Cul (Scheme 3.33) [71]. In the absence of Cul, a complicated mixture of products was obtained. Furthermore, the Cu-catalyzed reactions exhibited higher yields and higher selectivity than analogous reactions of alkynyl epoxides with lithium dialkylcup-rates [72], This method was applied to a reaction of allylmagnesium bromide with an alkynyl epoxide [73]. 

Although the iron-catalyzed synthesis of allenes from propargylic halides was reported by Pasto and coworkers in 1978 [67], little progress was achieved in this field until recently [68]. In 2003, Fiirstner and coworkers discovered propargylic epoxides as valuable substrates for the reaction with Grignard reagents in presence of catalytic amounts of Fe(acac)3 to generate 2,3-allenol derivatives (Scheme 5.24) [69]. 

Treatment of the epoxide (1) with Grignard reagents in the presence of copper(I) iodide gives, 6- -benzylidene-D-allal (2) in high yield (Scheme 1) C-4 epimers underwent the same reaction. ... 

A mechanistically related reaction occurs when epoxides react with Grignard reagents to produce alcohols. The carbon skeleton contains two more carbon atoms than the starting alkyl hahde. The sequence of reactions is shown below. 

We saw an example of nucleophilic ring opening of epoxides in Section 15 4 where the reaction of Grignard reagents with ethylene oxide was described as a synthetic route to primary alcohols... 

The reaction of Grignard reagents with epoxides is regioselective m the same sense Attack occurs at the less substituted carbon of the ring... 

In terms of cost, the effectiveness of the catalytic cycle in the ring closure makes this process economical in palladium. The first three steps in the reaction sequence -- ring opening of an epoxide by a Grignard reagent, converison of an alcohol to an amine with inversion, and sulfonamide formation from the amine — are all standard synthetic processes. 

B Reactions of Grignard Reagents WITH OXIRANES (EPOXIDES)... 

Rearrangement of several substituted chlorohydrins of fixed conformation has recently been reported by Curtin and Harder,3M and attention is directed to this interesting paper, since it is related to the abnormal reaction of a-haloketonos with Grignard reagents and hence pertinent to epoxide chemistry,... 

The characteristic ease with which ethylene oxides undi ruu nucleophilic attack or isomerization in tbe presence of Lewie acids made them obvious substrates for tbe org nometallic reagents intro duoed by Grignard 07 around the turn of the century, and subsequently named in his hunor. The earliest disclosure of a reaction between an epoxide and a Grignard reagent, however, bears the name of Blaise,1 who noted the formation of ethylene bromohydrin on troii merit of ethylene oxide with raethylmagneeium bromide. In the years... 

---