Styrenes dimethyl diazomalonate

Kondo maintained his interest in this area, and with his collaborators [62] he recently made detailed investigations on the polymerization and preparation of methyl-4-vinylphenyl-sulfonium bis-(methoxycarbonyl) meth-ylide (Scheme 27) as a new kind of stable vinyl monomer containing the sulfonium ylide structure. It was prepared by heating a solution of 4-methylthiostyrene, dimethyl-diazomalonate, and /-butyl catechol in chlorobenzene at 90°C for 10 h in the presence of anhydride cupric sulfate, and Scheme 27 was polymerized by using a, a -azobisi-sobutyronitrile (AIBN) as the initiator and dimethylsulf-oxide as the solvent at 60°C. The structure of the polymer was confirmed by IR and NMR spectra and elemental analysis. In addition, this monomeric ylide was copolymerized with vinyl monomers such as methyl methacrylate (MMA) and styrene. 

Catalytic cyclopropanation of alkenes with diazomalonates is sometimes carried out with copper powder, but it appears that copper(I) halide/trialkyl phosphite complexes (for a procedure see Houben-Weyl Vol. E19b, p 1113), bis(acetylacetonato)copper(II), " ° and tet-raacetatodirhodium can be employed more advantageously (Table 13, entries 7-9). For the cyclopropanation of styrene with dicyclohexyl diazomalonate, however, copper(I) triflate was the catalyst of choice, while intramolecular C —H insertion at the cyclohexyl ring took place in the presence of tetraacetatodirhodium. A detailed comparison of copper catalysts for the cyclopropanation of cyclohexene, 1-methyl- and 1,2-dimethylcyclohexene, (Z)- and ( )-hept-2-ene with dimethyl diazomalonate, including competitive reaction pathways such as allylic C-H insertion and carbene dimer formation, is available. The catalyzed interaction between diazomalonic esters and enol ethers leads to cyclopropanes in some cases (e.g. ethoxymethylenecyclohexane to dimethyl 2-ethoxyspiro[2.5]octane-l,l-dicarboxylate ) and to different products in other cases (e.g. 1-methoxycyclohexene, 2-methoxy-3,4-dihydro-2/7-pyran ). This behavior is attributed to the occurence of stabilized dipolar intermediates in these reactions. 

Notably, [Rh2(esp)2] (esp = a,a,a, a -tetramethyl-l,3-benzenedipropanaote) was also found to exhibit catalytic activity in the cyclopropanation reaction of styrene-type alkenes with dimethyl diazomalonate at room temperature with very low catalyst loading (0.1 mol%) (eq 42). The corresponding cyclopropanes were formed in good yields. In this reaction, alkene is employed as the limiting reagent, which is in contrast to many related reactions that an excess (>5 equiv) of alkenes was employed. 

As mentioned in the previous update, the as)unmetric cyclopropanation reaction was generally ineffective when dimethyl diazomalonate was used as carbenoid source the best ee value (50%) was reported in the cyclopropanation of styrene catalyzed by Rh2(45-MEAZ)4 (eq IS). Yet, recently the reaction of styrene with dimethyl diazomalonate in the presence of a chiral diene-rhodium catalyst was demonstrated. A catalytic amount (4 mol %) of NaBAr 4 [Ar = 3,5-bis(trilluoromethyl)phenyl] was employed for the generation of a cationic complex, and the reaction exhibited high enantioselectivity (eq 43). 

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