Bicyclopropyl derivatives

Bicyclopropyl (23) is a mixture of about equal amounts of the anti and the sc (gauche) conformer in the gas phase58. 1, r-dimethylbicyclopropyl59 (24), on the other hand, exists in the sc form with a dihedral angle of 58.0( 15) °. Equal ring bond lengths had to be assumed in the ED analysis (Table 2). Parameters obtained are consistent with the MM3 calculated values for 2362. 

The molecules of 25 have the same sc conformation with t 57.9° as gas-phase 24, and C2 symmetry in the orthorhombic Pbcn crystal60. Mean bond lengths are the same in the two molecules (Table 2). The cyano substituent causes a shortening of C2—C3 to 1.489 A in 25. Steric repulsion of gauche CH2 groups explains the widening of C3—Cl—C(N) 122.3(3)° relative to C2—Cl—C(N) 120.4(3)°, but Cl— C3 1.515 A is shorter than Cl—C2 1.526 A (corrected bond lengths)60. 

26 is the addition product of dichloroketene and an olefin63. The C4—Me bond is in syn bisecting position to the three-membered ring, and angles C4—Cl—C2 are slightly widened to 122.5°. The ring is nearly symmetric, the C—C bond (mean) 1.503 and the 

Cl —C4 bond 1.507(3) A are as usual (Table 2), and indicate no strain in this part of the molecule. 

The crystal of 23 is orthorhombic, space group Cmca. The molecules possess crystallographic 21m (C2h) point group symmetry, which involves the exact anti bisected form. This is the less stable form in the gas phase, as deduced from their relative abundance The deformation electron-density maps have been determined at 100 K by The 

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Addition of a second mole gives bicyclopropyl derivatives. 1,4 Addition is rare but has been reported in certain cases.Carbene adds to ketene to give cyclo-... 

In protic solvents, alkylbicyclopropylidenes 43e,f can be smoothly reduced with lithium to give a mixture of bicyclopropyl derivatives 227 a, b almost quantitatively [56 a]. The stereoselectivity of these reductions with dissolving lithium... 

TABLE 2. Structural parameters of alkyl cyclopropanes and bicyclopropyl derivatives ... 

Recently, a yn-bicyclopropyl derivative 112 as a single isomer with > 90 /o de has been prepared by following the Yamamoto protocol for asymmetric cyclopropanation. ... 

The reaction of the chromium complex of cyclopropyl(methoxy)carbene with an alkene results in the formation of bicyclopropyl derivatives 4 in good yield, accompanied occasionally by minor amounts of ring-opened products. 

The C-C double bond of (alk-l-enyl)cyclopropanes undergoes various cycloaddition reactions. The majority of the reactions are [2-1-2] and [4 + 2] types, but some [3 + 2] cycloadditions have been carried out. Furthermore, vinylcyelopropanes are readily converted to bicyclopropyl derivatives via a [2+1] type transformation which is discussed in Section 1.1.4. 

To interprete the PE spectra of these bicyclopropyl derivatives the Walsh model is suitable. It has been diown recently that for compounds with 6 values of zero degree the consideration of the tangential p orbitals only (see below) in the three-membered rings is sufficient. For those compounds, however, in which B also deviates considerable from zero the radially oriented 2p orbitals (see below) have to be con-... 

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