Cyclopentadiene, oxidative cycloaddition reaction with

Few isothiazoles undergo simple cycloaddition reactions. 4-Nitroisothiazoles add to alkynes (see Section 4.17.7.4). With 5-thiones (84) and dimethyl acetylenedicarboxylate, addition to both sulfur atoms leads to 1,3-dithioles (85) (77SST(4)339, 80H(14)785, 81H(16)156, 81H(16)595). Isothiazol-3-one 1-oxide and the corresponding 1,1-dioxide give normal adducts with cyclopentadiene and anthracene (80MI41700), and saccharin forms simple 1 1 or 1 2 adducts with dimethyl acetylenedicarboxylate (72IJC(B)881). 

The cycloaddition of allenes carrying an electron-withdrawing phosphorus substituent has also been studied [118]. Allenyl phosphine oxide 138 is prepared in a manner analogous to allenyl sulfoxide. The [4+ 2]-cycloaddition reaction of 138 with cyclopentadiene proceeded with a high endo selectivity. 

Chinese chemists have reported the synthesis of pentacyclo[4.3.0.0 , 0 ]nonane-2,4-bis(trinitroethyl ester) (88). This compound may find potential use as an energetic plastisizer in futuristic explosive and propellant formulations. The synthesis of (88) uses widely available hydroquinone (81) as a starting material. Thus, bromination of (81), followed by oxidation, Diels-Alder cycloaddition with cyclopentadiene, and photochemical [2 - - 2] cycloaddition, yields the dione (85) as a mixture of diastereoisomers, (85a) and (85b). Favorskii rearrangement of this mixture yields the dicarboxylic acid as a mixture of isomers, (86a) and (86b), which on further reaction with thionyl chloride, followed by treating the resulting acid chlorides with 2,2,2-trinitroethanol, gives the energetic plastisizer (88) as a mixture of isomers, (88a) and (88b). Improvements in the synthesis of nitroform, and hence 2,2,2-trinitroethanol, makes the future application of this product attractive. 

Tropolone has been made from 1,2-cycloheptanedione by bromination and reduction, and by reaction with N-bromosuccinimide from cyclo-heptanone by bromination, hydrolysis, and reduction from diethyl pimelate by acyloin condensation and bromination from cyclo-heptatriene by permanganate oxidation from 3,5-dihydroxybenzoic acid by a multistep synthesis from 2,3-dimethoxybenzoic acid by a multistep synthesis from tropone by chlorination and hydrolysis, by amination with hydrazine and hydrolysis, or by photooxidation followed by reduction with thiourea from cyclopentadiene and tetra-fluoroethylene and from cyclopentadiene and dichloroketene. - The present procedure, based on the last method, is relatively simple and uses inexpensive starting materials. Step A exemplifies the 2 + 2 cycloaddition of dichloroketene to an olefin, " and the specific oycloadduot obtained has proved to be a useful intermediate in other syntheses. " Step B has been the subject of several mechanistic studies, " and its yield has been greatly improved by the isolation technique described above. This synthesis has also been extended to the preparation of various tropolone derivatives. - " ... 

Key to method (A) exchange reaction with tin heterocycle (B) hydride addition to diyne (C) oxidation of saturated ketone (D) bromination-dehydrobromination by pyrolysis (E) reaction of RLi or ArLi with exocyclic M-Cl of preformed diene (F) ring expansion reaction from cyclopentadiene derivative (G) LiAlHi reduction of exocyclic M-Cl (H) carbene insertion into five-membered cyclo-pentadiene derivative. Doering-Hoffman method (I) 1,6-cycloaddition of GeCU. 

Diazene 19 was synthesized in the manner portrayed below. Thus, treatment of anhydride 20 with sodium borohydride selectively reduces one carbonyl to a methylene unit. Reduction of the resulting lactone with DIBAL followed by a Wittig reaction and oxidation with PCC afforded aldehyde 22. When treated with cyclopentadiene in the presence of diethylamine in methanol, 22 undergoes a smooth and efficient conversion to fulvene 23. Diels-Alder cycloaddition to the azodicarboxylate 24 proceeded rapidly, a characteristic of reactions with this electron deficient chlorinated dienophile [8]. Selective reduction of the endocyclic n bond using diimide generated in situ, followed by the electrochemical reductive cleavage of the biscarbamate led to diazene 19 [6]. 

Reports of studies on the reactions of diphosphenes have begun to appear. Like (137), (140) is stable towards methanol but is cleaved by hydrogen chloride. The less hindered (143) dimerizes at room temperature in a few hours, and gives cycloaddition products with Sg and cyclopentadiene (Scheme 11). Oxidation... 

DicWoroketene is particularly reactive, and reductive dechlorination of the product with zinc and acetic acid allows access to the cyclobutanone from formal addition of ketene itself. Thus, cycloaddition of dichloroketene with cyclopentadiene, followed by dechlorination and Baeyer-Villiger oxidation gave the lactone 173, a usehil precursor to various oxygenated cyclopentane products (3.117). Intramolecular cycloaddition reactions of ketenes can allow the formation of bicyclic and polycyclic products using otherwise unstable ketene intermediates. ... 

Various approaches to the assembly of the 1,3-dienes that engage in the Diels-Alder cycloaddition reactions leading to substrates for DPM and ODPM processes have been reported. Thus, for example. Yen and Liao demonstrated, during the course of a total synthesis of the Lycopodium alkaloid magellanine, that oxidation of acetovanillone (109) rScheme 9.151 with diacetoxyiodobenzene (DAIB) in the presence of methanol afforded the o-benzoquinone monoketal 110. The latter conpound engaged in an in situ Diels-Alder reaction with added cyclopentadiene (111) and the resulting adduct 112 proved to be an excellent substrate for the ODPM rearrangement reaction. Thus, photolysis of 112 as a solution in acetone afforded the pivotal tetracyclic diketone 113 in 92% yield. 

Reactions of methoxycarbonylformonitrile, furonitrile and substituted benzoni-trile oxides (4-Me, 4-OMe, 3-OMe, 4-C1, 3-C1, 2,4-di-Cl, 4-F as substituents) with dimethyl 7-(diphenylmethylene)bicyclo[2.2. l]hept-2-ene-5,6-dicarboxylate led exclusively to exo cycloadducts 82 (R = C02Me, 2-furyl, substituted phenyl), which, on irradiation with a low-pressure mercury lamp, afforded 3-azabicyclo [4.3.0]nonadiene-7,8-dicarboxylates 83 as the only products. The 1,3-dipolar cycloaddition, followed by a photorearrangement, provides a new method for obtaining tetrahydro-27/ -pyridine derivatives from cyclopentadiene (245). 

Analogously to the oxidation of A -alkoxycarbonylhydroxylamines, the oxidation of A -hydrox-yureas, performed with tetraalkylammonium periodate, gives nitrosocarbonyl compounds which undergo hetero-Diels-Alder cycloaddition with 1,3-dienes. A number of adducts 10 have been prepared and the reaction proceeds with total diastereoselectivity, although the yield has only been reported for cyclopentadiene and Ar-hydroxy-A"-phenylurea33. 

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