Cyclopropanation Diels-Alder adducts

The Diels-Alder reaction of methylenecyclopropane with cyclohexa-1,3-diene at 120°C gave the spirocyclopropanebicyclooctene in 50% yield.When cyclopentadiene and spiro[2.4]hepta-4,6-diene were used as dienes the respective spirocyclopropanenorbornenes were obtained. At 190°C, (chloromethylene)cyclopropane underwent [2 + 4] cycloaddition reactions with cyclopentadiene, furan and cyclohexa-1,3-diene to give the respective Diels-Alder adducts. The reaction of buta-1,3-diene and cyclohexa-1,3-diene with bicyclopropylidene as dienophile gave predominantly the [2 + 2] cycloadduct in addition to a small quantity of the Diels-Alder product. Cyclopentadiene, however, formed exclusively the dispirocyclo-propanenorbomene as result of a formal [2 + 4] cycloaddition. 

Phenylallylidene)- and (l-vinylallylidene)cyclopropane, generated in situ by the reaction of bicyclopropylidene with iodobenzene or vinyl iodide in the presence of palladium(ll) acetate, triphenylphosphane and triethylamine, reacted with methyl acrylate and dimethyl maleate, respectively, to give the expected Diels-Alder adducts. ... 

Diphenylmethylene)cyclopropane underwent a [4 + 2] cycloaddition reaction with maleic anhydride in which the C1,C2 bond of one phenyl group acted as part of the diene system. The primary methylenecyclohexadiene reacted with a second molecule of maleic anhydride to give a stable Diels-Alder adduct.For similar reactions see Section 5.2.3.1.2.2. 

Conflicting results were reported for the reaction of 1,3-diphenylisobenzofuran with benzocyclopropene. Reaction in chloroform (207 days) reportedly gave the unsymmetrical 5,10-diphenyl-10,ll-dihydro-5,10-epoxy-5//-dibenzo[a,c/lcycloheptene (7) in 71% yield,which was derived from addition of the furan to one of the lateral cyclopropane bonds. However, under similar conditions, other authors also report the formation of the isomeric exo and endo Diels-Alder adducts 6 and 8 in low yield.Under optimum conditions (tetrahydrofuran, 80 °C, 3 days), the enr/o-adduct 6 was isolated in 52% yield.The formation of the unsymmetrical adduct 7 was ascribed to a radical reaction, similar to that observed in the addition of buta-1,3-diene to benzocyclopropene. 

Opening of the cyclopropane with sodium to franj-2,8-menthadiene (526). Further treatment with sodium (on sodium carbonate or alumina) rearranged the latter to isoterpinolene [2,4(8)-menthadiene (527)]. 1(7),8-Menthadiene (528) is a potential intermediate for l(7)-menthen-9-al (529) although this aldehyde is also not yet reported in nature. The diene 528 was made, for example, by a Wittig-type reaction on the Diels-Alder adduct 530 (R = O) of me yl vinyl ketone and 2-trimethylsily 1-1,3-butadiene (9, R = SiMe3). Treatment of 530 (R... 

A variety of diverse synthetic methods have been empioyed for the preparation of cyclopropane (1 j. Schlatter and Demjanov and Dojarenko pyrolyzed cyclopropyltrimethylammonium hydroxide at 320°C using platinized asbestos as the catalyst. About equal amounts of cyclopropene (1) and cyclopropyidimethylamine are formed, contaminated with some dimethyl ether and ethylene. Treatment with dilute hydrochloric acid removed the amine from the gas stream and 1 was separated from the other products by gas chromatography. Alder-Rickert cleavage of the Diels-Alder adduct formed from cycloheptatriene and dimethyl acetylenedicarboxylate resulted only in the formation of a polymer and trace amounts of 1. A simple approach by Closs and Krantz based on the synthesis of 1-methylcyclopropene involved the addition of allyl chioride to a suspension of sodium amide in mineral oil at 80°C. Under the conditions employed, 1 could readily escape from the reaction mixture. Though a number of variations were tried, the yield of 1 never exceeded 10%. 

Diels-Alder activation volume, 138, 139, 145 Diels-Alder adduct uses, 145, 146 Diels-Alder with anthracene, 98 Diels-Alder with cyclopentadiene, 87 Diels-Alder with cyclopropane compounds, 132 Diels-Alder entropy of activation, 138 Diels-Alder molecular orbital picture, 140-143 Diels-Alder with nonconjugated dienes, 132 Diels-Alder with poly(furfuryl methacrylate), 472 Diels-Alder reaction dienophile, 103, 120, 138, 140, 142... 

Hexamethyl[3]radialene (25) does not undergo Diels-Alder-reactions with the typical electron-poor dienophiles, probably because of the full substitution at the diene termini. With TCNE, however, a violet-blue charge-transfer complex is formed which disappears within 30 min at room temperature to form a 1 1 adduct (82% yield) to which structure 55 was assigned9. Similar observations were made with tris(2-adamantylidene)cyclopropane (34), but in this case cycloaddition product 56 (81% yield) was identified its allenic moiety is clearly indicated by IR and 13C NMR data12. 

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],... 

Where the carbon-carbon double bond is a part of an aromatic system, in general, cyclopropanation of diazoketones results in the formation of unstable cyclopropane adducts. For example, Saba140 has shown that in the intramolecular cyclopropanation of diazoketone 57 the norcaradiene ketone 58 can be detected by low-temperature NMR and can be trapped in a Diels Alder reaction with 4-phenyl-l,2,4-triazoline-3,5-dione (equation 69). In addition, Wenkert and Liu have isolated the stable norcaradiene 60 from the rhodium catalysed decomposition of diazoketone 59 (equation 70)105. Cyclopropyl ketones derived from intramolecular cyclopropanation of hetereoaromatic diazoketones are also known and two representative examples are shown in equations 71 and 72106. Rhodium(II) compounds are the most suitable catalysts for the cyclopropanation of aromatic diazoketones. 

TiCl4 is used extensively as a Lewis acid in numerous organic transformations, forming adducts that mediate reactivity. Such reactions include Diels Alder, 54,355 hetero Diels Alder,356 cyclization of olefinic aldehydes,357 Flosomi Sakurai allylic coupling reactions,358 cyclopropanations,359 chal-cogen-Baylis Flillman,360 Mukaiyama Aldol reactions,36 363 reductions of ketones to alcohols 364 and stereoselective nucleophilic additions to aldehydes.365... 

The nitroisoxazole (35) underwent Diels-Alder reaction with 2,3-dimethyl butadiene to form the adduct (36) (Equation (5)) <90JOC1227>. The nitroisoxazole ester (37) with 2-diazopropane yielded the bicyclic cyclopropane (39), via an unstable adduct (38) (Scheme 4) <87cci077>. The same ester... 

The Site Selectivity of 1,3-Dipolar Cycloadditions. The site selectivity of 1,3-dipolar cycloadditions is the same as for the Diels-Alder reactions in Section 6.5.2.6. To give just two examples, the unsaturated ester 6.356 reacts with diazomethane at the 4,5-double bond, to give the adduct 6.357,871 and diazoacetic ester adds to the terminal double bond of 1-phenylbutadiene 6.358, giving the pyrazoline 6.359, with the product actually isolated after the loss of nitrogen being the corresponding cyclopropane.872... 

When the Michael receptors are chiral, diastereoselective cyclopropanation reactions are possible. Treatment of an enan-tiomerically pure (+)-dicyclopentadienone with EDS A gave the eA o-cyclopropane product in 88% yield in >99% ee. Thermolysis of this adduct gave, via a retro-Diels-Alder reaction, an optically active (>99% ee) cyclopentenone in 82% yield (eq 8), ... 

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