ChemInform Abstract: KERNMAGNETISCHE RESONANZ KLEINER RINGE 13. MITT. CYCLOPROPYLIDENE

Pierre, Jean‐Louis; Vidal, Michel; Arnaud, Paul; Gey, C.

doi:10.1002/chin.197032081

Cited by 2 publications

(2 citation statements)

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“…The aqueous layer was extracted with pentane (3 x 25 ml). After drying of the combined extracts with sodium sulfate and distillation of the solvent and the residue at 30 and 16 Torr we obtained 610 mg ( 123 (14), 81 (61), 67 (loo), 55 (27), 41 (36), 39 (17). r-3,t-5-Diethyl-3,5-dihydro-t-3.~-5-dimethyl-4-methylene-4H-~yr-azole (trans-2): The procedure for cis-2 described above was followed exactly yielding 560 mg (68%) of a colourless liquid, b.p.…”

Section: -2 2 1 "C (Ref2s) 110--112°c)mentioning

confidence: 99%

Retention of Configuration and E/Z Stereoselectivity in the Photolysis of cis‐ and trans‐Tetraalkyl‐4‐methylene‐1‐pyrazolines

Quast

Jakobi

1991

Chem. Ber.

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The isomeric 4-methylene-1-pyrazolines cis-and trans-2 are synthesized by a Wittig reaction from the pyrazolin-4-ones cisand trans-1, respectively. Direct irradiation with 350-nm light of cis-2 affords the alkylidenecyclopropanes cis-8, (E)-and (4-9 (64: 17: 19) besides molecular nitrogen and small amounts of the 4-methylenepyrazolidine cis-7 as a result of photoreduction. Under the same conditions, trans-2 is converted into trans-8 as well as (E)-and (4-9 (64: 14: 22). The configurations of cis-and trans-8 have been established by means of a 1,3-dipolar cycloaddition with mesityl nitrile oxide which furnishes two cycloadducts from cis-8, e.g. cis-14A and B, but only one cycloadduct from trans-8, viz. trans-14. The configurations of (4-and (3-9 have been assigned on the basis of homoallylic 'H,'H coupling constants and nuclear Overhauser ~ experiments. The results demonstrate that, on the least-motion paths leading to cis-and trans-8, the configuration of the ring substituents in cis-and trans-2 is completely retained. Of the non-least-motion products (E)-and (a-9 the latter is favoured regardless of the configuration of the precursors cis-and trans-2 though the extent of (Z) selectivity depends on that configuration. The results are interpreted in terms of bis-orthogonal trimethylenemethane diradicals as primary intermediates from which irreversible paths bifurcate. Cyclization yields cis-8 (from cis-2) or trans-8 (from trans-2) and 9V-bond rotations afford two diastereomeric mono-orthogonal trimethylenemethane diradicals [(E)-and (3-181 which eventually cyclize to the corresponding non-least-motion products (4-9 and (z)-9.For a long time, stereochemical evidence has contributed significantly to the elucidation of chemical reaction pathways3). In particular, the extent of retention of configuration has served as a demanding criterion for the distinction of one-step from two-step cycloaddition and cycloreversion reactions. Retention of configuration has been associated with either concertedness or two-step reactions via intermediates which cyclize very fast compared to the rate of bond rotation4). Van Auken and Rinehart, Jr., were the first to apply this criterion to the photoextrusion of molecular nitrogen from cisltrans-isomeric 1 -pyrazolines and observed a preference for retention of configuration in the cyclopropane products'). Bartlett and Porter studied the stereochemical consequences of the photoextrusion of an azo group from a six-membered ring6). An excellent review by Givens summarizes the stereochemical results of the photoextrusion of small molecules ' ). No attention, however, has been paid as yet to the steric course of ring closure following the loss of molecular nitrogen from 4-alkylidene-I -pyrazolines. This is all the more surprising as their thermolysis and photolysis have been thoroughly studied in numerous investigations8-12) which have received additional impetus from the interest in trimethylenemethane diradicals 13). We now report that the photolysis of diastereomeric 4-methylene-1-pyrazo...

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Section: -2 2 1 "C (Ref2s) 110--112°c)mentioning

confidence: 99%

Retention of Configuration and E/Z Stereoselectivity in the Photolysis of cis‐ and trans‐Tetraalkyl‐4‐methylene‐1‐pyrazolines

Quast

Jakobi

1991

Chem. Ber.

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“…,J(H, CH,) in a cyclopropane derivative is 6.2Hz (8). An INDO MO FPT calculation, using a standard geometry (9) for the methyl group, the electron diffraction geometr for the cyclopropane fragment (lo), and 1.54 1 for the exocyclic C-C bond, gives J, = 17.0 and Jo = 2.47Hz.…”

Section: Conformational Distributionmentioning

confidence: 99%

Concerning the conformational distribution in isopropylcyclopropane

Schaefer¹,

Sebastian²,

Wasylishen³

1982

Can. J. Chem.

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A partial analysis of the 400 MHz 1H nmr spectrum of isopropylcyclopropane yields 8.6 ± 0.2 Hz for the vicinal proton–proton coupling constant between a cyclopropyl proton and the methine proton of the isopropyl group. The fractional population of the s-trans conformer is estimated as 0.65 ± 0.l0 at 300 K, in reasonable agreement with molecular mechanics and INDO MO computations of the energies of the gauche and trans forms.The conformational preference of this molecule is similar to that in n-butane and in vinylcyclopropane but contrasts with that in biisopropyl and bicyclopropyl.

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ChemInform Abstract: KERNMAGNETISCHE RESONANZ KLEINER RINGE 13. MITT. CYCLOPROPYLIDENE

Cited by 2 publications

References 0 publications

Retention of Configuration and E/Z Stereoselectivity in the Photolysis of cis‐ and trans‐Tetraalkyl‐4‐methylene‐1‐pyrazolines

Retention of Configuration and E/Z Stereoselectivity in the Photolysis of cis‐ and trans‐Tetraalkyl‐4‐methylene‐1‐pyrazolines

Concerning the conformational distribution in isopropylcyclopropane

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