20968-70-1Relevant academic research and scientific papers
Synthesis of Carbo- and Heterocyclic Cyclopropindenes via Cycloaddition of Dienes to Cyclopropenes
Mueller, Paul,Miao, Zhongshan
, p. 1826 - 1836 (1994)
The heterocyclic cyclopropindene 19 was synthesized via cycloaddition of diene 10 to the cyclopropene 11a and subsequent base-induced aromatization.While 19 is isolable, although very short-lived, the oxa analogue 18 decomposed under the conditions required for its preparation.The difluoro derivatives 14 and 15, in which the heterocyclic moiety is saturated, are accessible by the cycloaddition approach, but the corresponding dichlorides are again not isolable.Cyclopropindenes carrying substituents at C(4) have been obtained via cycloaddition of 22b to 1-bromo-2-chlorocyclopropene.The key step of the sequence is a double Curtius degradation of the cycloadduct 23b to the ketone 27a.While aromatization of the alcohol 27b provided the cyclopropindenol 28b, the reaction failed with 27a.Attempts to convert 28b to 1,3-dihydrocyclopropindene (25) via the methanesulfonate 28d failed.
Competitive 1,2-C Atom Shifts in the Strained Carbene Spiro[3.3]hept-1-ylidene Explained by Distinct Ring-Puckered Conformers
Rosenberg, Murray G.,Schrievers, Theodor,Brinker, Udo H.
, p. 12388 - 12400 (2016/12/23)
Spiro[3.3]hept-1-ylidene is a markedly strained carbene reaction intermediate that was generated by high-vacuum flash pyrolysis (HVFP) of the corresponding p-tosylhydrazone sodium salt. Five hydrocarbons were produced from the Bamford-Stevens reactant in 82% overall yield. The carbene undergoes two [1,2]-sigmatropic rearrangements via competing 1,2-C atom shifts. Ring-contraction yields cyclopropylidenecyclobutane, while ring-expansion affords bicyclo[3.2.0]hept-1(5)-ene. The ring contraction is regiospecific despite the formation of some 1-methylenespiro[2.3]hexane. It does not originate from the carbene under HVFP conditions. Instead, it comes from a methylenecyclopropane-type rearrangement of chemically activated cyclopropylidenecyclobutane. Similarly, some chemically activated bicyclo[3.2.0]hept-1(5)-ene rearranges to 1,2-dimethylenecyclopentane via electrocyclic ring-opening. Accounting for the conversion of primary products to secondary ones, relative yields indicate that ring-contraction within the carbene prevails over ring-expansion by a factor of 6.7:1. Computational chemistry was used to assess the structures, conformations, energies, strain energies, transition states, and activation energies of these rearrangements with the goal of explaining product selectivities. The dual-ringed carbene is predicted to assume four distinct geometric conformations that have a bearing on transition-state selection. The reactive cyclobutylidene units of two conformers are significantly puckered, like cyclobutylidene itself, while those of the other two are flatter. The selectivity of the title carbene is compared with that of spiro[2.3]hex-4-ylidene.
Enantioselective formal synthesis of tridemethylisovelleral
R?me, Daniel,Johansson, Martin,Sterner, Olov
, p. 635 - 638 (2007/10/03)
A simple and efficient synthetic route to the bicyclic α,β-unsaturated β-keto ester methyl (3aS,7aS)-6-oxo-2,3,3a,6,7,7a-hexahydro-1H-indene-5-carboxylate, a versatile intermediate in the synthesis of biologically active unsaturated 1,4-dialdehydes, is described. The synthesis includes a chirality introducing nonenzymatic asymmetric desymmetrization (ADS) reaction of a cyclic meso-anhydride 4 and a modified Hofmann method for preparing exocyclic dienes. The ester was synthesized in a moderate overall yield (19%) from 6 and with an excellent enantioselectivity (>90%).
Hetero-Diels-Alder and cheletropic additions of sulfur dioxide to 1,2-dimethylidenecycloalkanes. Determination of thermochemical and kinetics parameters for reactions in solution and comparison with estimates from quantum calculations
Monnat, Frederic,Vogel, Pierre,Sordo, Jose Angel
, p. 712 - 732 (2007/10/03)
Below -60° and without catalyst, 1,2-dimethylidenecyclopentane (16), 1,2-dimethylidenecyclohexane (13), 1,2-dimethylidenecycloheptane (17), and 1,2-dimethylidenecyclooctane (18) add to sulfur dioxide in the hetero-Diels-Alder mode, giving the correspondin
Evidence for 2-Hexene-1,6-diyl Diradicals Accompanying the Concerted Diels-Alder Cycloaddition of Acrylonitrile with Nonpolar 1,3-Dienes
Li, Yufei,Padias, Anne Buyle,Hall, H. K.
, p. 7049 - 7058 (2007/10/02)
The spontaneous reactions of a series of alkyl 1,3-dienes with acrylonitrile (AN) were investigated.Reproducible spontaneous copolymerizations were shown to compete with the expected concerted cycloadditions.For dienes which exist in s-cis/s-trans equilibrium, both copolymer and cycloadduct are formed.Kinetic measurements show that the alternating copolymerization and cycloaddition are two independent paralell second order reactions.With 1,3-cyclohexadiene and 1,2-dimethylenecyclohexane, for which s-gauche is in equilibrium with s-cis, copolymerization still competes with cycloaddition.The s-trans-locked verbenene forms only copolymer, while s-cis-locked cyclopentadiene and 1,2-dimethylenecyclopentane form only cycloadduct rapidly.Our explanation involves a 2-hexene-1,6-diradical, formed by combination between the terminal carbons of the s-gauche or s-trans diene and acrylonitrile.This does not cyclize but initiates copolymerization.Competitively s-cis conformer undergoes classical concerted addition.
Cleavage vs Rearrangement Ratios and Secondary Deuterium Kinetic Isotope Effects in the Thermolysis of Conformationally Fixed Cisoid Vinylcyclobutanes
Gajewski, Joseph J.,Paul, Gitendra
, p. 1986 - 1989 (2007/10/02)
The first-order rate constants for the thermally induced retro 2+2 cleavage and rearrangement of 5-methylenespirononane occur in a 1:2 ratio.In contrast, a 2:1 ratio of these rate constants is usual from conformationally unbiased vinylcyclobutanes.Comparison of the activation parameters suggests that the rearrangement in unbiased systems results from an unfavorable entropy of activation which suggests that the rearrangement is concerted.For the rearrangement of 5-methylenespirooctane, the secondary deuterium kinetic isotope effect at the exo-methylene carbon (kH/kD2) is 1.086 +/- 0.023.This is also consistent with concert in the rearrangement where exo-methylene rotation contributes to the reaction coordinate.The secondary KIE for cleavage of 5-methylenespirooctane is 1.025 +/- 0.027.
Reaction of Photochemically Generated Dibromocarbene with 1,2-Dimethylenecycloalkanes. 1,4 Addition Is Real
Le, Nguyet Anh,Jones, Maitland,Bickelhaupt, Friedrich,Wolf, Willem H. de
, p. 8491 - 8493 (2007/10/02)
Photochemically or thermally generated dibromocarbene adds to a variety of 1,2-dimethylenecycloalkanes and to norborndiene to give 1,2 and 1,4 addition products.The ratios of the products of the two addition types match those found from dibromocarbene generated from bromoform.Dibromocarbene is capable of 1,4 addition.
Cycloadditions of Substituted 1,2-Dimethylenecyclopentanes. - The Influence of Methyl Groups on the Rate of Diels-Alder Reactions
Sustmann, Reiner,Daute, Peter,Sauer, Ralf,Sommer, Angelika,Trahanovsky, Walter S.
, p. 1551 - 1558 (2007/10/02)
The preparation of methyl-substituted 1,2-dimethylenecyclopentanes and their reactivity in (4+2) cycloadditions with α,β-unsaturated carboxylic esters and nitriles is studied.In kinetic measurements the methyl groups show a moderately rate-enhancing effect.The results are compared with those for analogously substituted butadienes.Whereas 1,1-dimethylbutadiene reacts with TCNE to form a mixture of (2+2) and (4+2) cycloadducts, the correspondingly substituted 1,2-dimethylenecyclopentane gives only the (4+2) adduct. - Key Words: Cycloadditions/ Diels-Alder reactions
Reactions of 2,3-Dimethylenebutadiene Dianion with Electrophiles. Synthesis and Conformations of 2,3-Disubstituted-1,3-butadienes
Bates, Robert B.,Gordon, Bernard,Highsmith, Thomas K.,White, James J.
, p. 2981 - 2987 (2007/10/02)
Reactions of 2,3-dimethylenebutadiene dianion 1 with monofunctional electrophiles were found to provide the best routes to symmetrically substituted 1,3-butadienes such as 2c - n.Evidence that at least some of these reactions go by single electron-transfer mechanisms is presented.Possible mechanisms for the formation of some unusual byproducts are discussed.Reactions of 1 with dichlorides and dibromides were found to provide the best routes to most 1,2-dimethylenecycloalkanes 3, the corresponding dimers 4 and trimers 5, and 1,1-dimethyl-3,4-dimethylene-1-metallacyclopentanes 26.From their UV spectra, the dienes 2 contain about 60percent transoid conformations, except 2,3-dimethyl-1,3-butadiene (2a) which shows about 100percent and 2,3-dineopentyl-1,3-butadiene (2h) which shows about 30percent. 1,2-Dimethylenecycloalkanes 3 display cisoid conformations in rings smaller than 9-membered and transoid conformations in rings larger than 11.When the ring size exceeds 15, the homoallylic methylene groups on both sides are also anti coplanar.With rings larger than about 30, the next methylene group on each side is also anti coplanar, and when the ring size exceeds about 45, an additional methylene on each side is anti coplanar.
