Methylenecyclopropanes group

The strength of the carbon-carbon bond adjacent to a difluoromethylene group IS hardly affected by the presence of fluorine on the cyclopropyl ring When heated, 2,2 difluoromethylenecyclopropane undergoes methylene-cyclopropane rearrangement [/2 ] Under kinetic control, 2,2 difluoro 1 methylenecyclopropane and (difluoromethylene)cyclopropane are formed in a 2 1 ratio, although the latter IS slightly more stable [129] (equation 27)... 

For electron withdrawing substituted methylenecyclopropanes (R = EWG) the stabilization of the negative charge by the EWG group as in TS-A justifies the high regioselectivity observed. 

More recently, Yang et al. [123] have examined a new approach in which a reactive functional group was introduced into polyolefins using methylenecyclopropane (Scheme 27). Thus, ethylene (1.0 atm) was copolymerized with methylenecyclopropane (0.25-2.5 ml) using [LnH(C5Me5)2]2 (Ln = Sm, Lu) in toluene at 25 °C. It was shown that 10-65 units of exo-methylenes were incorporated per 1000-CH2- units and the resulting polymer had an Mw of 66-92 x 103, yet its Mw/Mn was > 4. 

While thermodynamically, the direct metalation of cyclopropane can be envisioned from a synthetic point of view, this approach has been rarely used. A major obstacle appears to be kinetics which can be overcome by incorporation of a hydroxyl group (see Eq. 16)17). In special cases, such as bicyclo [1.1.0] butane and methylenecyclopropane (Eq. 17) 18) the enhanced thermodynamic acidity is aceom-... 

Metalations with organolithium compounds, 8, 6 26, 1 27, 1 Methylenation of carbonyl groups, 43, 1 Methylenecyclopropane, in cycloaddition reactions, 61, 1... 

In the light of experimental difficulties associated with the identification of intermediates, a MINDO/3 quantum-mechanical study of the singlet state ( a2) of the cyclobutylidene to methylenecyclopropane rearrangement has been carried out. It has been proposed that the whole process is initiated by electrophilic attack from the C3 methylene group of cyclobutylidene at the empty p atomic orbital on the Cl carbene site, so that a shift of electron density towards Cl can take place to give the bicyclobutane-like nonclassical carbene intermediate 4. Finally, the bicyclobutane intermediate 4 undergoes a symmetry-allowed conrotatory bond-fission process to generate methylenecyclopropane. The activation enthalpy calculated for the two steps is 8 kcal mol-1.2... 

Use of excess of reagents and prolonged reaction times lead to dialkylation, dimerization, isomerizations and cross-coupling reactions (equation 187). In the presence of methoxy groups in the side chain, alkylation is followed by migration of the double bond to form the thermodynamically more stable methylenecyclopropanes (equation 188). 

De Meijere and co-workers have extended the scope of this process by applying this palladium-mediated multicomponent reaction to the bicyclopropylidene 72 as the alkene partner (Scheme 8.33). In this case, the intermolecular trapping of 7r-allyl palladium intermediate 73 with a soft carbonucleophile or with primary or secondary amines affords only products 74 having a methylenecyclopropane end group [78],... 

Bis(phosphoranimine) ligands, chromium complexes, 5, 359 Bis(pinacolato)diboranes activated alkene additions, 10, 731—732 for alkyl group functionalization, 10, 110 alkyne additions, 10, 728 allene additions, 10, 730 carbenoid additions, 10, 733 diazoalkane additions, 10, 733 imine additions, 10, 733 methylenecyclopropane additions, 10, 733 Bisporphyrins, in organometallic synthesis, 1, 71 Bis(pyrazol-l-yl)borane acetyl complexes, with iron, 6, 88 Bis(pyrazolyl)borates, in platinum(II) complexes, 8, 503 Bispyrazolyl-methane rhodium complex, preparation, 7, 185 Bis(pyrazolyl)methanes, in platinum(II) complexes, 8, 503 Bis(3-pyrazolyl)nickel complexes, preparation, 8, 80-81 Bis(2-pyridyl)amines... 

Creary, X. Wolf, A. Miller, K. Facile autoxidation of 2-(4-hydroxyphenyl)-3,3-dimethyl-methylenecyclopropane. The radical stabilizing ability of the phenoxide group. Org. Lett. 1999, 1, 1615-1618. 

---