Insertion reactions magnesium carbenoids

A very interesting synthetic method of bicyclo[n.l.O]alkanes from cychc ketones via this 1,3-C,H insertion of magnesium carbenoid as a key reaction was reported (equation 22) . 1-Chlorovinyl p-tolyl sulfoxide (76) was synthesized from cyclopentadecanone and chloromethyl p-tolyl sulfoxide in three steps in high overall yield. Lithium enolate of tert-butyl acetate was added to 76 to give the adduct 77 in quantitative yield. a-Chlorosulfoxide (77) in a toluene solution was treated with i-PrMgCl in ether at —78 °C and the reaction mixture was slowly warmed to 0°C to afford the bicyclo[13.1.0]hexadecane derivative 79 in 96% yield through the reaction of the intermediate magnesium carbenoid 78. 

Carbon-hydrogen (C,H) insertion reaction of magnesium carbenoids... 

It is worth noting that use of i-PrMgCl in ether (not in THF) and toluene as solvent for the reaction is essential for the reaction to proceed. Otherwise, the protonated product of magnesium carbenoid 78, obtained as by-product, was very difficult to separate from the desired compound (79). Interestingly, the 1,3-C,H insertion reaction is highly regioselective. 

An intramolecular 1,5-C,H insertion reaction was reported from substituted bromo-iodoalkane and halogen-magnesium exchange reaction (equation 24) °. Indeed, treatment of bromoiodoalkane (86) with i-PrMgCl in ether at —78°C to —20°C resulted in the formation of magnesium carbenoid 87. The 1,5-C,H insertion of 87 took place to afford a cyclopentane derivative (88) however, the yield was not satisfactory. 

The formation of w-propyl and -butyl iodides is a side reaction in the preparation of cyclopropane derivatives from olefins by the reaction with diethylzinc and em-diiodoalkanes 163). This side reaction is enhanced by the presence of lithium or magnesium halides, and was explained in terms of insertion of the zinc carbenoid into the carbon-iodine bond 245). 

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