“…The issue of the relative reactivity of olefinic and acetylenic dienophiles bearing an identical activating group had been taken up with separate substrates. − In our case, the two unsaturated sites (“o” and “a”) would be directly linked. We here note that Kocienski et al have reported that the reaction of an enyne, activated by a single ester substituent on the alkyne moiety, with a Danishefsky-type diene afforded the product formed from addition to the double bond in about 40% yield 5a.…”
The paper describes the course of cycloadditions of Diels-Alder dienophiles containing linked enyne sites, each substituted with activating groups. Consistently, it was found that in the enyne cases the Diels-Alder reaction occurred specifically at the acetylenic center. Furthermore, it was found that the regiochemical sense of the cycloaddition was apparently determined by the remote activating group bound to the olefinic site. This remote acrylyl group totally dominated the course of the cycloaddition, relative to the activating group bound directly on the acetylene site. Explanations for these findings at the computational level are provided. The computations also rationalize the strong preference for cycloaddition to occur at the acetylene linkage and encompass the otherwise surprising regiochemical dominance by the remote ester on the olefinic site. The high selectivities available through such reactions provide important new opportunities in the synthesis of orsenillate type substructures that are found in a variety of natural products of contemporary interest.
“…The issue of the relative reactivity of olefinic and acetylenic dienophiles bearing an identical activating group had been taken up with separate substrates. − In our case, the two unsaturated sites (“o” and “a”) would be directly linked. We here note that Kocienski et al have reported that the reaction of an enyne, activated by a single ester substituent on the alkyne moiety, with a Danishefsky-type diene afforded the product formed from addition to the double bond in about 40% yield 5a.…”
The paper describes the course of cycloadditions of Diels-Alder dienophiles containing linked enyne sites, each substituted with activating groups. Consistently, it was found that in the enyne cases the Diels-Alder reaction occurred specifically at the acetylenic center. Furthermore, it was found that the regiochemical sense of the cycloaddition was apparently determined by the remote activating group bound to the olefinic site. This remote acrylyl group totally dominated the course of the cycloaddition, relative to the activating group bound directly on the acetylene site. Explanations for these findings at the computational level are provided. The computations also rationalize the strong preference for cycloaddition to occur at the acetylene linkage and encompass the otherwise surprising regiochemical dominance by the remote ester on the olefinic site. The high selectivities available through such reactions provide important new opportunities in the synthesis of orsenillate type substructures that are found in a variety of natural products of contemporary interest.
“…It was found that HCP readily adds to the olefinic bonds of the conjugated system, for example, maleic anhydride and acrylonitrile. Similary, HCP condenses with allylic dienophiles and halogenated olefins only at elevated temperatures 5, 6…”
Section: Introductionmentioning
confidence: 98%
“…In this reaction cyclodienes are reacted with dienophiles and form adducts simply by mixing the components at room temperature or by gentle warming. However, in cases with either unreactive dienes or dienophiles more vigorous conditions may be necessary 4, 5. The Diels–Alder reaction is reversible and many adducts dissociate into their components at quite a low temperature 3, 5.…”
Section: Introductionmentioning
confidence: 99%
“…However, in cases with either unreactive dienes or dienophiles more vigorous conditions may be necessary 4, 5. The Diels–Alder reaction is reversible and many adducts dissociate into their components at quite a low temperature 3, 5. In these cases better yields are obtained by using an excess of one of the reactants or a solvent from which the adduct readily separates 3.…”
ABSTRACT:The present investigation has been achieved in accordance with the Diels-Alder reaction (1,4 cycloaddition) to produce a new halogenated bicyclic adduct. orthoBromoallylbenzoate is a new dienophile that was prepared in a pure form, and its structure was confirmed. The DielsAlder syntheses of hexachlorocyclopentadiene and the new dienophile were studied to determine the optimum condensation reaction conditions under a temperature range of 90 -160°C, reaction times of 1-8 h, and molar diene/dienophile ratios from 1:1 to 5:1 as a consequence. The optimum conditions reached were a temperature of 140°C, an initial diene/dienophile molar ratio of 3:1, and a duration time of 6 h. The maximum stoichometric yield under these optimum conditions (82.5%) was obtained.
“…Compounds I-IV, the physicochemical constants of which are given in Table 1, were produced by the procedures that we described in earlier papers [6][7][8].…”
As is known, polychlorinated bicyclic compounds are widely used as monomers and modifi ers for the production of heat and fi re-resistant polymeric materials and elastomers, and also fi reproofi ng additives to fl ammable thermoplastic materials. The fi reproofi ng action of polychlorinated compounds is connected with the fact that, during heating, they split off atomic chlorine, which is an effective fi re retardant. Their introduction into epoxy resins makes it possible to produce heat-resistant composites [1-5].
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