Magnesium cyclopropylidenes

A. Magnesium Cyclopropylidenes as Intermediates in the Doering-LaFlamme Allene Synthesis... 

At first, 1-chlorocyclopropyl phenyl sulfoxide (93) was synthesized from the olefin 92 in three steps in good yield. Treatment of sulfoxide 93 with 2.5 eq of /-PrMgCl in THF at —78 °C for 5 min followed by quenching with CD3OD afforded the deuteriated chlorocy-clopropane (95) in 78% yield with high deuterium incorporation. From this experiment, it was proved that the intermediate of the reaction is a magnesium cyclopropylidene species 94 (equation 26). 

Then, the magnesium cyclopropylidene (94) generated at —78 °C was slowly warmed to —60°C and stirred at this temperature for 3 h. Deuterolysis of the reaction mixture with CD3OD afforded the chlorocyclopropane in 81% yield with 95% D-content. From... 

The electrophilic reaction of magnesium cyclopropylidene (113) with Ai-lithioaryl-amines was reported (equation 31) . Thus, electrophilic reaction of magnesium cyclopropylidene (113) derived from 112 with iV-lithio iV-methyl p-anisidine resulted in the formation of a-amino-substituted cyclopropylmagnesium (119) in good yield. Methanol-ysis of the reaction mixture with CH3OD gave a-deuteriated Af-cyclopropyl-Af-methyl-p-anisidine (120) in 82% yield with 98% D-content. 

The reaction of 113 with several Af-lithioamines was investigated and the results are summarized in Table 5. Af-Methylaniline, p-chloro-Af-methylaniline and Af-benzyl-p-anisidine gave 60-67% yield of the desired Af-cyclopropyl arylamines. Diphenylamine gave the desired product however, the yield was not satisfactory. Interestingly, dibenzy-lamine did not afford the desired product at all. This result indicated that the magnesium cyclopropylidene (113) only reacts with Af-lithio arylamines. The reaction of 113 with Af-lithio nitrogen-containing heterocyclic compounds was also studied. From the results shown in Table 5, the yields of the reaction are variable as a function of the heterocyclic compounds used. 

TABLE 5. Reaction of magnesium cyclopropylidene (113) derived from 1-chlorocy-clopropyl phenyl sulfoxide (112) with Al-hthio amines... 

Ultrasonically dispersed lithium, magnesium and sodium have all been used in the synthesis of allenes and cyclopropylidenes from dihalocyclo-propanes [121] (Scheme 52). 

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