Diene syntheses double

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. 

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. 

Now, dienes with shielded donble bonds can be involved in diene synthesis. The presence of donor gronps at the double bond normally prevents its involvement in conventional Diels-Alder condensations. These reactions do take place with the cation-radicals. Cyclic adducts are formed in high yields (80-90%) and under mild conditions. Polymerization, which usnally decreases the yield is inhibited completely within the framework of the cation-radical variant (Bellville et al. 1981). The stereoselectivity of the addition, which is usually typical for diene condensation, does not change in the cation-radical version and even increases. The positional selectivity also increases. The regiose-lectivity is enhanced, as well. Bauld et al. have discovered and explained these effects (Bellville and Banld 1982, Bellville et al. 1981, 1983, Banld and Pabon 1983, Pabon and Banld 1984). 

This method affords a-pyrone in quantity and in good yield not achieved previously.3 The compound has considerable possibilities in Diels-Alder reactions, such as a decarboxylative double diene synthesis.5... 

We have already mentioned the bulky f-butoxide—ideal for promoting E2 as it s both bulky and a strong base (p aH - 18). Here it is at work converting a dibromide to a diene with two successive E2 eliminations. Since dibromides can be made from alkenes (you will see how in the next chapter), this is a useful two-step conversion of an alkene to a diene, synthesis of a diene by a double E2 elimination... 

An alternative approach to diene synthesis using the basic methodology of the Julia coupling has been studied by Otera. Polyenes (445) and alkynes (443) can be formed by double elimination of the sulfone and the hydroxy component (Scheme 58). ° ... 

Zimmerman and Paufler heated a-pyrone with excess methyl vinyl ketone and achieved decarboxylative double diene synthesis of the diacetylbicyclo[2.2.2]-2-... 

The Diels-Alder reaction (diene synthesis) is the addition of compounds containing double or triple bonds (dienophiles) to the 1,4 positions of conjugated dienes with the formation of six-membered hydroaromatic rings. Hydrocarbons most often used in the reaction are 1,3-butadiene, cyclopentadiene, and isoprene, and dienophiles used include maleic anhydride, acrolein, and acrylic acid. The literature on this process is thoroughly reviewed by Alder (1), Kloetzel (59), Holmes (48), and Norton (82). 

A study comparing, under a range of conditions, diene synthesis by the two alternative Wittig routes, allylic ylide-saturated aldehyde (route 1) and reactive ylide-a,P-unsaturated aldehyde (route 2), has been reported. 9 por the system chosen (Scheme 2) the reactive ylide-a,P-unsaturated aldehyde route is clearly preferred in that the stereochemistry of the new double bond can be controlled more easily and there is little or no isomerisation of the double bond already present in the aldehyde. A route to symmetrically substituted polyenes containing an odd or even number of double bonds has been reported (Scheme 3).20 The Wittig reactions of ylides derived from... 

A double diene synthesis occurs with benzoquinone. With 2 molecules of cyclohexadiene, for instance, this affords the 1,4,5,8-diethanoanthracene ring system the resulting l,4,4a,5,8,8a,9a,10a-octahydro-l,4,5,8-diethanoanthra-quinone readily loses four hydrogen atoms, to give the 1,4,5,8-tetrahydro compound and, when that is heated, it spits off ethylene to afford anthraquinone ... 

SCHEME 3. a) Synthesis of dimethyl disulfide (DMDS) derivatives of isolated double bonds (monounsaturated compounds or double bonds separated by four or more CH2 groups) b) DMDS adducts from dienes with double bonds separated by 1, 2, or 3 CH2 groups c) DMDS adducts from conjugated double bonds. 

N,N-Betaines s. Aminimides Betti 1,3-oxazine ring closure 10, 578 22, 778 Bi... s. a. Di... Bicyclo[1.1.0]butane ring opening, double -, diene synthesis with - 31, 654 Bicyclo[5.3.0]decane ring s. Azulenes... 

The same synthesis is not effective for the synthesis of 2,3-disubstituted-butanediols-2,3 as dehydration of such glycols formed mixtures of dienes whose double bond is frequently located as an internal double bond. In such cases the reaction of choice is pyrolysis of the butane-dioldiacetates-1,4 which give exclusively and without... 

Protection of carbon-carbon double bonds by diene synthesis... 

A -oxazol-2-ones 28, 365 phthalimides 27, 403 carbon-carbon double bonds by diene synthesis 28, 631... 

Otto Diels and Kurt Alder won the 1950 Nobel Prize in Chemistry for their discovery and development of the diene synthesis. This reaction would later on be called the Diels/Alder reaction or [4+2]-cycloaddition. 23 years before, the two chemists had demonstrated a new reaction type the addition of appropriate systems, soon to be named dienophiles, to reaction partners containing conjugated double bonds and hence classified as conjugated dienes [1]. 

In Eq. (4.2) it is implied th t the residual double bond during a diene synthesis is formed at the b-c position. Although this is true generally, often the double bond may migrate to a thermodynamically more stable position to give isomeric products. The case in point is the reaction of l,4-diphenyl-l,3-butadiene 15 with MA. In this reaction, two isomeric products 16 and 17 are obtained. 

The structure and stereochemistry of the adducts formed in this reaction depend on the mutual orientation of the diene and dienophile which, in its turn, is determined by the form of the transition compound. According to modern ideas, the transition state in the diene synthesis is a cyclic complex in which the system of double bonds of the diene and the dienophile are located in parallel planes A and B (Fig. 3a) and the four reaction centers are present in one plane. 

Another feature of the diene synthesis, spatial directivity, arises where the diene has substituents or a ring in the 1,4-positions and the dienophile is unsymmetrical with respect to plane D passing through the four reaction centers (Fig. 3c). If the substituent of the dienophile in the transition state will be located on the same side of plane D as the double-bond system of... 

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