“…In cases where the radical center of the cyclopropylcarbinyl moiety is embedded in the bicyclo[ n .1.0] system, there tends to be a strong stereoelectronic preference for exocyclic ring opening. − The situation is quite different when the radical center is exo to the bicyclic ring system (e.g., 3 ). Here increased conformational mobility of the radical-bearing center allows SOMO overlap with either of the β-cyclopropyl bonds; consequently, both homoallylic radicals 4 and 6 are accessible. , 2 …”
The viability of utilizing 1-bicyclo[4.1.0]heptanylmethyl radical (3) to serve as a progenitor of seven-membered carbocycles was examined. Rate constants for the rearrangement of this radical to
3-methylenecycloheptyl radical (4) and 2-methylenecyclohexyl-1-methyl radical (6) were measured
using the competition method of 3 with thiophenol over the temperature range of −75 to 59 °C.
Arrhenius functions were calculated for the conversions of 3 to 4 and 3 to 6 and found to be log(k/s-1) = (12.38 ± 0.20) − (5.63 ± 0.23)/θ and log(k/s-1) = (11.54 ± 0.32) − (5.26 ± 0.37)/θ,
respectively. The rate constants for these conversions at 25 °C are 1.86 × 108 s-1 and 5.11 × 107
s-1, respectively. Hence, the seven-membered ring-expanded carbocycle is formed 3.6 times faster
at 25 °C than the nonexpanded species. This suggests that the 1-bicyclo[4.1.0]heptanylmethyl radical
system may be synthetically useful in seven-membered ring-forming methodology. Preliminary
theoretical examination of this radical system qualitatively predicted the experimentally determined
energies of activation: PMP4/6-31G*//HF/6-31G* ΔE
a (3 → 6 − 3 → 4) = 3.0 kcal/mol with zero
point energy correction. The HF/6-31G* optimized reaction coordinate stationary points suggest
cyclopropyl substituent eclipsing interactions play an important role in determining the kinetic
outcome of these rearrangements.
“…In cases where the radical center of the cyclopropylcarbinyl moiety is embedded in the bicyclo[ n .1.0] system, there tends to be a strong stereoelectronic preference for exocyclic ring opening. − The situation is quite different when the radical center is exo to the bicyclic ring system (e.g., 3 ). Here increased conformational mobility of the radical-bearing center allows SOMO overlap with either of the β-cyclopropyl bonds; consequently, both homoallylic radicals 4 and 6 are accessible. , 2 …”
The viability of utilizing 1-bicyclo[4.1.0]heptanylmethyl radical (3) to serve as a progenitor of seven-membered carbocycles was examined. Rate constants for the rearrangement of this radical to
3-methylenecycloheptyl radical (4) and 2-methylenecyclohexyl-1-methyl radical (6) were measured
using the competition method of 3 with thiophenol over the temperature range of −75 to 59 °C.
Arrhenius functions were calculated for the conversions of 3 to 4 and 3 to 6 and found to be log(k/s-1) = (12.38 ± 0.20) − (5.63 ± 0.23)/θ and log(k/s-1) = (11.54 ± 0.32) − (5.26 ± 0.37)/θ,
respectively. The rate constants for these conversions at 25 °C are 1.86 × 108 s-1 and 5.11 × 107
s-1, respectively. Hence, the seven-membered ring-expanded carbocycle is formed 3.6 times faster
at 25 °C than the nonexpanded species. This suggests that the 1-bicyclo[4.1.0]heptanylmethyl radical
system may be synthetically useful in seven-membered ring-forming methodology. Preliminary
theoretical examination of this radical system qualitatively predicted the experimentally determined
energies of activation: PMP4/6-31G*//HF/6-31G* ΔE
a (3 → 6 − 3 → 4) = 3.0 kcal/mol with zero
point energy correction. The HF/6-31G* optimized reaction coordinate stationary points suggest
cyclopropyl substituent eclipsing interactions play an important role in determining the kinetic
outcome of these rearrangements.
“…Further transannular interactions in monoacetals (12) and (13) could be dramatically demonstrated by LiAlH, reduction of the free carbonyl group. In both compounds the primarily formed secondary alcohols, (15) and (16) respectively, undergo an acid-catalysed rearrangement to give a pentacyclo derivative, (17) and (18), respectively, bearing a bridged acetal ether and a primary alcohol, as shown by 'H n.m.r. spectroscopy, and confirmed either by preparation of the pnitrobenzoate or by oxidation to the corresponding aldehyde.…”
Regioselective bromination of Deslongchamps's diketone (6), followed by base-induced transannular cyclization, leads to f e t r a c y c l 0 [ 5 . 3 . 0 .~~~. 0~*~] decane-5,8-dione ( 8 ) , together with minor amounts of the isomeric tetracyclo[5.2.1 .02,6.03~8]decane-4,9-dione (9). The chemistry and photochemistry of the monoacetals of (8) have been studied, and structural assignments confirmed either by X-ray diffraction analysis or 2 D n.m.r. spectroscopy.Cage-structure compounds and their derivatives are of great interest in connection with a number of topics, such as the testing of the scope and limitations of synthetic methods, the determination of structure-reactivity relationships, and the theoretical and experimental estimation of strain energies. More recently, the lipophilic character of spherical hydrocarbon molecules has led to additional interest in the pharmacological properties of these compounds.2 b 3 a 4( 2 ) 10 general strategy are found in the synthesis of b~llvalene,~ t w i~t a n e ,~ cubane,' and dodecahedrane.6 In this context, properly functionalized derivatives having the skeleton of endo-tricycl0[5.2.l.O~*~]decane (1) are of interest for the synthesis of tetra-and penta-cyclo C,, systems (Scheme 1).
Whereas photochemical intramolecular[2 + 2lcycloaddi-tions of derivatives of compound (1) have been an important synthetic starting point for bis-homocubane (2) derivative^,^ + E d 3 * cy; 4 4 0 ( 4 ) Scheme 1.Since compounds with cage structures have usually a substantial amount of strain energy, a general strategy for the synthesis of these compounds relies on the preparation of key intermediates which have adequate geometry and functionalization in order to create, through some irreversible process, the bond(s) which mostly contribute to the total strain of the molecule by means of proximity effects. Examples of such a nothing is known concerning the selective bond formation between C(3)-C(9), C(4)-C(9), and C(5)-C(9) which would lead to the tetracyclic skeletons (3), (4), and (5), respectively. In fact, derivatives of (3) and (4) have been obtained by selective reduction of one of the bonds of bishomocubane (2).8 On the other hand, derivatives of (5), and even the hydrocarbon itself have been synthesized starting from an intermediate with the
“…However, under aerated conditions, irradiation of a solution of lg (480 mg) and xanthene (800 mg) in benzene (60 mL) for 40 h by light from a 300-W high-pressure Hg-arc lamp gave reaction products. After removal of the solvent, isolation of the residue by column chromatography on silica gel gave 2-methyl-1,4-naphthoquinone (20,85 Reaction of lh with Xanthene. Under completely deaerated conditions, irradiation of a mixture of lh and xanthene dissolved in benzene gave no photoproduct.…”
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