1,3-Dienes Diels-Alder

Cyclodienes. These are polychlorinated cycHc hydrocarbons with endomethylene-bridged stmctures, prepared by the Diels-Alder diene reaction. The development of these insecticides resulted from the discovery in 1945 of chlordane, the chlorinated adduct of hexachlorocyclopentadiene and cyclopentadiene (qv). The addition of two Cl atoms across the double bond of the ftve-membered ring forms the two isomers of chlordane [12789-03-6] or l,2,4,5,6,7,8,8-octachloro-2,3,3t ,4,7,7t -hexahydro-4,7-methano-lJT-indene, QL-trans (mp 106.5°C) and pt-tis (32) (mp 104.5°C). The p-isomerhas signiftcantiy greater insecticidal activity. Technical chlordane is an amber Hquid (bp 175°C/267 Pa, vp 1.3 mPa at 25°C) which is soluble in water to about 9 fig/L. It has rat LD qS of 335, 430 (oral) and 840, 690 (dermal) mg/kg. Technical chlordane contains about 60% of the isomers and 10—20% of heptachlor. It has been used extensively as a soil insecticide for termite control and as a household insecticide. 

Cyclopentadiene contains conjugated double bonds and an active methylene group and can thus undergo a Diels-Alder diene addition reaction with almost any unsaturated compound, eg, olefins, acetylene, maleic anhydride, etc. The number of its derivatives is extensive only the reactions and derivatives considered most important are discussed. 

As the last reaction of equation 99 suggests, trifluoromethyl substituted furans are themselves reactive Diels-Alder dienes [722] (equation 102)... 

Keywords Facial selection. Orbital phase, Secondary orbital interaction. Orbital unsymmetrization. Ketones, Olefins, Diels-Alder dienophiles, Diels-Alder dienes, Michael acceptor. Amine nitrogen atom... 

In order to smdy the effect of perturbation arising from spiro-conjugation on the chemical reactivities, in particular the facial selectivities, sterically unbiased dienes (96 and 97) based on fluorenes in spiro geometry have been synthesized [165]. These dienes react as Diels-Alder dienes with several dienophiles (maleic anhydride (MA), A-phenylmaleimide (PMI), A-phenyl-l,3,5-triazoUne-2,4-dione (PTD) and iV-methyl-l,3,5-triazoline-2,4-dione (MTD)). 

Diels-Alder diene + dienophile + heat => adduct... 

Electron-deficient 1,3-dienes are potentially interesting Diels-Alder dienes. In our study with different kinds of olefins, we observed that 2-(phenylsulfonyl )-l,3-d1enes show a duality in their Diels-Alder cycloaddition reactions, giving [4+2] adducts with both electron-deficient and electron-rich olefins. This dual reactivity of the 2-(phenylsulfony1)-l,3-dienes in [4+2] cycloaddition increases the role they can play in organic synthesis. 

The cyclopropanated furanone 32 was found to behave as a Diels-Alder diene. Thus, 32 reacts with maleic anhydride (33) to give a tetracyclic adduct 34 which is formed endoselectively (Scheme 9) (93SL415). The latter adduct is a spiroannulated butenolide related to naturally occurring sesquiterpenes [85AG(E)94 85TL5453],... 

Bis(trifluoromethyl)-i,2,4,5-tetrazme, which is synthesized from 2,5-bis(trifluoromethyl)-l,3,4-oxadiazole by addition of hydrazine followed by mild oxidation [720] (equation 100), is a reactive and very interesting Diels-Alder diene [727] Its normal reaction is to add the dienophile and then to extrude N2 to form a diazene, as exemplified by its reaction with propyne [720] (equation 101)... 

However, when the diene system is constrained to the s-cis conformation by a cyclic framework, the effective concentration of the s-cis diene is much higher than for acyclic dienes, which have the s-cis conformer as a minor component of the rotomeric equilibrium. Such conformationally constrained dienes react much more easily and are excellent Diels-Alder dienes. Examples are cyclopentadi-enes, 1,3-cyclohexadienes, and furans. 

Diels-Alder diene + alkene/alkyne decarboxylation lose C02 from a carboxylic acid hydroxylation add -OH nitration add -N02... 

Benzopyran-3-ones are not generally isolated, but they are useful as reactive intermediates and especially as reactive Diels-Alder dienes. The generation of 3/7-2-benzopyran-3-ones is usually achieved by the cyclodehydration of ortfo-acylphenylacetic acids carried out in the presence of acetic anhydride (Scheme 222) <1996CHEC-II>. 

Dimethylhexa-2,4-diene and a 4,6-dienone undergo photo-addition to give a mixture of isomeric 4,5-adducts of type (302), including 4a,5a-, 4a ,5/3-, and 4/3,5/3-adducts. 4-Methylpenta-1,3-diene adds in the same orientation. The mechanistic and stereochemical features are discussed both dienes are of the type which function as substituted alkenes rather than as Diels-Alder dienes.242... 

HOCOCH can t be used as a Diels-Alder diene because it is linear. The end carbons are too far apart to be able to react with a dienophile in a cyclic transition state. Furthermore, the product of Diels-Alder addition would be impossibly strained, with two sp-hybridized carbons in a six-membered ring. 

In addition to being a very reactive Diels-Alder diene, l,3,4,5,6,7-hexaphenylbenzo[f]furan was reported to be highly fluorescent in toluene solution, as well as in its solid state. This benzo[f]furan may therefore be used as electron transport material in an organic light-emitting diode <2002SM247>. 

Acyclic ( -pentadienyl)Fp complexes also behave as Diels-Alder dienes in some cases, although two other reaction pathways compete. With TCNE and maleic anhydride, (17 R = H, Me) undergoes cycloaddition in moderate yields. Highly electron-deficient alkynes, on the other hand, undergo Fe bond insertion reactions reminiscent of SO2 reactions with ( -allyl)Fp complexes, to give (30). Finally, when the pentadiene is disubstituted at C-5, the Diels-Alder route is effectively blocked, and [3 + 2] cycloadditions result with TCNE at the 2,3-double bond. ... 

Two quite specific methods have been employed for the synthesis of imidazo[2,l- ]-[l,3,5]thiadiazines. In the condensation of l,2-diphenylimidazoline-4,5-dione (726) with a thiocarbonyl isocyanate such as (727), the isocyanate added to (726) in the manner of a Diels-Alder diene to produce (728) (67CB2064). 

Homoannular dienes e.g. i) readily add excited oxygen in a reaction which is the photochemical equivalent of the Diels-Alder diene-addition reaction fyjJ. The resulting epidioxides e.g. 2) are sufficiently stable for isolation/although they are fairly reactive [72]. 

As with the simple heterodienes, the electron-deficient heteroaromatic azadienes have proven ideally suited for 4Tt participation in LUMOdiene-controlled Diels-Alder reactions. In fact, it was Ae recognition of this electron-deficient nature of heteroaromatic azadienes that led to the proposed and demonstrated rate acceleration that may accompany the reversal of the electronic properties of the Diels-Alder diene-dienophile partners and subsequently led to the full investigation of the LUMOdiene-controlled Diels-Alder reaction. 

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