Organoaluminums methylene

A highly convenient and versatile cyclopropanation method has been devised which involves treatment of olefins with different organoaluminum compounds and alkylidene iodide under mild conditions [93]. Although Miller found that cyclopropane formation by use of EtsAl-methylene iodide in cyclohexene proceeds in quite disappointing yields [94], Yamamoto and Maruoka reached the conclusion that the intermediate dialkyl(iodomethyl)aluminum species 97 is responsible for the cyclopropanation of olefins and that it readily decomposes in the absence of olefins or in the presence of excess trialkylaluminum. Hence the use of equimolar amounts of trialkyl-aluminum and methylene iodide in the presence of olefins is essential for the achievement of reproducible results in the cyclopropanation process. In addition, because di-alkylaluminum halide can also be used as a cyclopropanation agent, the use of half an equivalent of trialkylaluminum is not detrimental (Sch. 61). 

The organoaluminum-mediated cyclopropanation had unique selectivity not observable in Simmons-Smith type reactions [95], Treatment of geraniol with i-Bu3Al (2 equiv.)-methylene iodide (1 equiv.) in CH2CI2 at room temperature for 5 h produced cyclopropanation products in 75 % combined yields in the ratio 76 1 4. Consequently, methylene transfer by the aluminum method occurs almost exclusively at the C(6)-C(7) olefinic site far from the hydroxy group of geraniol and the C(2) -C(3) ole-finic bond was left intact. In sharp contrast, the zinc method resulted in the opposite regioselectivity via hydroxy-assisted cyclopropanation, as shown in Sch, 62. 

The organoaluminum-mediated cyclopropanation exhibited unique selectivity which is not observable in the Simmons-Smith reaction and its modifications [79]. Treatment of geraniol with /-BuiAI/methylene iodide in CH2CI2 at room temperature... 

In the field of frustrated Lewis pair chemistry, organoaluminum compounds are often employed as the Lewis acid of the pair to great effect Just as aluminum is a substitute for boron in this case, carbenes are often substituted for the standard phosphines as mentioned in Section 15.5.1. Zhang et al. [137] used several frustrated Lewis pair combinations (A1(C6F5)3 with a variety of phosphines and carbenes) to facilitate the polymerization of methyl methacrylate, a-methylene-y-butyrolactone, and y-methyl-a-methylene-y-butyrolactone. Even combinations that form classical Lewis acid/base adducts rather than FLPs could still exhibit excellent polymerization activity. 

Prim, alcohols from methylene compounds—Organoaluminum compounds s. 11, 713 s.a. A. 629, 241 (1960)... 

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