Magnesium carbenoids generation

On the other hand, when this reaction was carried out with 1-chlorovinyl p-tolyl sulfoxide derived from unsymmetrical dialkyl ketone 167 with Af-lithio 1-aminonaphthalene (entries 7 and 8), Z-ortho-alkenylated arylamine Z-171 was obtained as the main product from both vinyl sulfoxides with low stereoselectivity. The stereospecificity and stereoselectivity mentioned above are explained from the high configurational stability of the magnesium carbenoids generated from 1-chlorovinyl p-tolyl sulfoxides derived from a,/ -unsaturated ketones. 

A. Generation of Magnesium Carbenoids by Halogen-Magnesium Exchange Reaction... 

Magnesium carbenoids (5 and 6) were generated from a geminal diiodoalkane by diastereoselective iodine-magnesium exchange reaction with isopropylmagnesium halide in THF at —78°C for 45 min (Scheme 1). Subsequent reaction of the magnesium... 

As mentioned above, the configuration of the magnesium carbenoid is rather stable at low temperature chiral Grignard reagents having over 90% ee could be generated from optically active 1-chloroalkyl aryl sulfoxides (Scheme 4)20-22... 

Thus, magnesium carbenoid 38, generated from 1-chloroalkyl phenyl sulfoxide (37) in THF at —65°C with 2.8 eq of i-PrMgCl, reacts with a-sulfonyl lithium carbanion to lead to 1,2-di- and 1,1,2-trisubstituted olefins (60). Yields are better in such conditions as compared to the reaction described in equation 14. 

Satoh, T. Takano, K. Ota, H. Someya, H. Matsuda, K. Koyama, M. Magnesium alkyl-idene carbenoids generation from 1-halovinyl sulfoxides with Grignard reagents and studies on the properties, mechanism, and some synthetic uses. Tetrahedron 1998, 54, 5557-5574. 

The magnesium alkylidene carbenoid generated occurs in equilibrium between... 

A. Generation and Nucleophilic Property of Magnesium Alkylidene Carbenoids, the Fritsch-Buttenberg-Wiechell Rearrangement... 

Stereochemistry of this reaction is also quite interesting. Thus, both geometrical isomers of 1-chlorovinyl p-tolyl sulfoxides (165-167) were synthesized from 2-cyclohexenone, methyl vinyl ketone and 2-heptanone respectively, and the corresponding magnesium alkylidene carbenoids were generated and treated with A-lithio aniline or A-lithio 1-aminonaphthalene. The results are summarized in Table 9. 

Treatment of magnesium alkylidene carbenoids, which were generated from 1-chlorovinyl /)-tolyl sulfoxide 161 with isopropylmagnesium chloride at —78°C in toluene, with AT-lithioindazole 162 (or pyrazole) gave N-alkenylated indazole 163 in moderate yield (Scheme 5) <2005TL4855>. Reaction of lithiopyrazole gave the N-alkenylated pyrazole but in a lower yield. 

---