Dienes syntheses

Compounds containing a double or triple bond, usually activated by additional unsaturation (carbonyl, cyano, nitro, phenyl, etc.) In the ap position, add to the I 4-positions of a conjugated (buta-1 3-diene) system with the formation of a ax-membered ring. The ethylenic or acetylenic compound is known as the dieTwphile and the second reactant as the diene the product is the adduct. The addition is generally termed the Diels-Alder reaction or the diene synthesis. The product in the case of an ethylenic dienophile is a cyctohexene and in that of an acetylenic dienophile is a cyctohexa-1 4-diene. The active unsaturated portion of the dienophile, or that of the diene, or those in both, may be involved in rings the adduct is then polycyclic. 

The last example is an interesting application of the diene synthesis, for the adduct upon dehydrogenation (most simply by the action of oxygen upon its solution in alcoholic potash) yields 2 3-dimethylantbraquinone. 

The mechanism of the diene synthesis appears to involve an electron transfer from the diene to the dienophile, .e., it is initiated by an ionic reaction. The following scheme may represent the addition of 2 3-dimethylbutadiene to maleic anhydride ... 

In the Diels-Alder reaction (in older literature referred to as the diene synthesis ) a six-membered ring is fonned through fusion of a four-tt component, usually a diene and a two-7C component, which is commonly referred to as the dienophile (Scheme 1.1). 

The synthesis of natural products containing the quinonoid stmcture has led to intensive and extensive study of the classic diene synthesis (77). The Diels-Alder cycloaddition of quinonoid dienophiles has been reported for a wide range of dienes (78—80). Reaction of (2) with cyclopentadiene yields (79) [1200-89-1] and (80) [5439-22-5]. The analogous 1,3-cyclohexadiene adducts have been the subject of C-nmr and x-ray studies, which indicate the endo—anti—endo stereostmcture (81). 

Azabicyclo[2.2.0]hexa-2,5-diene, pentakis-(pentafluoroethyl)-synthesis, 2, 304 2-Azabicyclop.2.0]hexadiene reactivity, 7, 360 thermal isomerization, 7, 360 2-Azabicyclo[2.2.0]hexa-2,5-diene synthesis, 2, 304 1 -Azabicyclo[3.2.0]hexadiene synthesis, 7, 361 1 - Azabicyclo[2.2.0]hexane reactions, 7, 344 ring strain... 

O. Diels (Kiel) and K. Alder (Cologne) discovery and development of the diene synthesis. 

Mention must also be made of an interesting reaction (103 —> 104) that makes use of the isoxazole nucleus of anthranil as a diene in the reaction with A-phenylmaleimide. This instance is of considerable interest, for it has proved impossible to introduce into the diene synthesis other derivatives with a noncondensed isoxazole ring. ... 

The reaction investigated by Diels and Alder in 1928 was not new, examples had been known for several years [6]. Early work on the dimerization of tetra-chloropentadienone was conducted by Zincke in 1893 and 1897. In 1906, Albrecht described the product of addition of p-benzoquinone to one or two molecules of cyclopentadiene. Albrecht assigned erroneous formulas to these addition products, but they were later shown to be typical products of the diene synthesis by Diels and Alder. Ruler and Josephson reported the addition products formed by iso-prene and 1,4-benzoquinone in 1920. This research laid the ground work for Diels and Alder. 

The total synthesis of palytoxin (1) is a landmark scientific achievement. It not only extended the frontiers of target-oriented synthesis in terms of the size and complexity of the molecules, but also led to new discoveries and developments in the areas of synthetic methodology and conformational analysis. Among the most useful synthetic developments to emerge from this synthesis include the refinement of the NiCh/CrC -mediated coupling reaction between iodoolefins and aldehydes, the improvements and modifications of Suzuki s palladium-catalyzed diene synthesis, and the synthesis of A-acyl vinylogous ureas. 

Dienes, synthesis of 731, 953, 956 Dienoic acids, synthesis of 675 Dienones, synthesis of 780 Dienyl sulphoxides, synthesis of 279, 810, 959... 

Barluenga J., Suarez-Sobrino A., Lopez L. A. Chiral Heterosuhstituted 1,3-Buta-dienes Synthesis and [4 + 2 Cycloaddition Reactions Aldrichimica Acta 1999 32... 

Aversa M. C., Barattucci A., Bonaccorsi P. and Giannetto P. Chiral Sulfinile-1,3-dienes-Synthesis and Use in Asymmetric Reactions Tetrahedron Asymmetry 1997 9 1339-1367... 

The choice of the acyl substituent X for Diels-Alder reactions of l-N-acylamino-l,3-butadicnes depends on the particular synthetic problem. The acyl substituent has a moderate effect on the cycloaddition reactivity of these dienes, and also determines what amine unmasking procedures are required. As a result of their stability and the variety of amine deprotection procedures available, " the diene carbamates are the components of choice in most cases. A particularly attractive aspect of the diene synthesis detailed here is the ability to tailor the amino-protecting group... 

Monodehydrohalogenation of allylic halides is another classical method for diene synthesis24. This method is complementary to double dehydrohalogenation as both the 1,2-dihalides and allylic halides are readily accessed from alkenes. The commonly employed protocol for diene synthesis, particularly for cyclic 1,3-dienes, is through the allylic monobromination of the alkene with A-bromosuccinimide or related reagents followed by dehydrobromination with hindered bases such as DBN or DBU (equation l)25. 

Trost and coworkers have devised a stereocontrolled 1,3-diene synthesis employing a palladium-catalysed decarboxylative elimination procedure from allylic acetates carrying carboxylic acid functionality ji- to the acetate group (equation 18)48. This decarboxylative elimination strategy has been applied to the synthesis of an insect pheromone, codlemone48a and the ethyl ester of vitamin A carboxylic acid (Table 5)48b. 

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