Magnesium carbenoid electrophilic

Carbenoids have both a nucleophilic and an electrophilic nature. This is one of the most striking characteristics of carbenoids. Especially, electrophilic reaction of magnesium carbenoids with carbon and nitrogen nucleophiles has recently received much attention and various new interesting synthetic methods have appeared. 

The electrophilic reaction of magnesium carbenoids with Af-lithio aryiamines was found to give non-stabiUzed a-amino-substituted carbanions (equation 17). Treatment of magnesium carbenoid 38 with 3.5 eq of Af-lithio Af-methylaniline at —70 °C followed... 

The reaction of iodomethyl carboxylates with PrMgCl in THF/N-butylpyrrolidi-none (NBP) (5 1) at -78°C affords the corresponding magnesium carbenoids, which react with a variety of electrophiles (Scheme 3.111) [138]. 

From a synthetic organic chemistry point of view, the electrophilic nature of magnesium alkylidene carbenoids is much more interesting than their nucleophilic nature. Satoh and coworkers found that treatment of 1-chlorovinyl p-tolyl sulfoxide (147) with an excess of PhMgBr in THF at —85 to —50 °C for 2 h followed by CD3OD gave the deuterio styrenyl derivative 150 in 80% yield with a complete deuterium incorporation (equation 37) ° . 

The electrophilic reaction of magnesium alkylidene carbenoids with other nucleophiles than the original Grignard reagent can also be carried out. For example, treatment of magnesium alkylidene carbenoid 157, derived from 147, with a-sulfonyl lithium carbanion afforded allenes 159 in moderated yields (equation 39/. ... 

Magnesium alkyUdene carbenoids were found to be reactive with different nucleophiles to give new alkenyhnagnesium compounds which could be trapped with electrophiles. As a whole, novel methods for the synthesis of tri- or tetrasubstimted olefins from the 1-chlorovinyl p-tolyl sulfoxides in a one-pot reaction are realized. 

TABLE 12. Synthesis of enyne 183 from magnesium alkylidene carbenoids 134a with lithium acetylides and electrophiles... 

TABLE 14. Synthesis of vinyl sulfides (186) by the reaction of magnesium alkyUdene carbenoids with lithium p-toluenethiolate followed by some electrophiles... 

Satoh and coworkers further investigated this reaction and found that, in some cases, magnesium /3-oxido carbenoids gave better results. Trapping of the enolate intermediates with several electrophiles was successfully carried out and a new method for the synthesis of one-carbon expanded cyclic a,a-disubstituted ketones from lower cyclic ketones was realized. An example using 1,4-cyclohexanedione mono ethylene ketal (195) as a representative cyclic ketone is shown in Table 15. ... 

Thus, a-sulfinyl lithium carbanion of 1-chloroethyl p-tolyl sulfoxide was reacted with 1,4-cyclohexanedione mono ethylene ketal (195) to afford the adduct (196) in quantitative yield. The adduct was treated with ferf-butylmagnesium chloride (magnesium alkoxide was initially formed) followed by isopropylmagnesium chloride to result in the formation of magnesium /3-oxido carbenoid 197. The /3-oxido carbenoid rearrangement then takes place to give one-carbon expanded magnesium enolate 198. Finally, an electrophile was... 

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