Cyclopentadiene diene synthesis with

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). 

Novel organometallics have been prepared via metal atom synthesis since the 1970s. Especially interesting have been diene reactions with early transition metal atoms. Cyclopentadiene on cocondensation with metal atoms reacts with Cr through a bis(cyclopentadienyl)chromiumdihydride intermediate to yield chromocene. For Mo and W, the intermediate species can be isolated. Labeling studies with Cp H and Cp D indicate that oxidative addition of the C-H bond to M occurs stepwise (- Cp MH CP2MH2) (see Oxidative Addition). 

R)- and (S)-f-Butyl-5-methylene-l,3-dioxolan-4-one, a Chiral a-Alkoxy Acrylate. It is also possible to introduce an ex-ocyclic double bond onto the dioxolanone ring, as in compounds (9)-(ll), derived from lactic and malic - acids. These a,3-unsaturated carbonyl derivatives are acceptors for radical additions and undergo cycloadditions with dienes and heterodienes. The Diels-Alder adduct (12) of ent-(9) with cyclopentadiene is formed with exo selectivity (96 4) and serves as aprecursor to norbomenone (13). Cycloadduct (14), obtained from methylenedioxolanone (9) and an open-chain triene, is also the result of an exo addition and is used in tetronolide synthesis. ... 

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). 

Synthesis. - Cycloadditions. The azadiene (26) behaves as a dienophile with cyclopentadiene but as a diene with acyclic 1,3-dienes and with cyclohexa-... 

The use of ketene equivalents in 4- -2-cycloaddition reactions for organic synthesis has been reviewed. " a-Carbonyl ketenes behave as dienes in Diels-Alder reactions with 4-aryl-2-methyl-2,3-dihydro-l,5-benzothiadiazepines to yield regiospecific cycloadducts. The reactions of diphenylketene with cyclic ( -cw)-l,3-dienes such as cyclopentadiene and cyclohexadiene initially yield the Diels-Alder adducts, which are converted into the Staudinger cyclobutanones by [3,3]-sigmatropic rearrangementsl-Benzyl-l,3-diazabuta-l,3-dienes react with ketenes to produce the 4 - - 2-cycloadducts, substituted l-benzyl-4-(benzylidenimino)-4-phenylazetidin-2-ones, which rearrange into the more stable 5,6-dihydro-3//-pyrimidin-4-ones. The formal 4 - - 2-cycloaddition reaction of ketenimines has been used to synthesize benzoimidazo[l,2-Z ]isoquinolines. ... 

A key transformation in Corey s prostaglandin synthesis is a Diels-Alder reaction between a 5-(alkoxymethyl)-l,3-cyclopenta-diene and a ketene equivalent such as 2-chloroacrylonitrile (16). As we have already witnessed in Scheme 3, it is possible to bring about a smooth [4+2] cycloaddition reaction between 5-substituted cyclopentadiene 15 and 2-chloroacrylonitrile (16) to give racemic 14 as a mixture of epimeric chloronitriles. Under these conditions, the diastereomeric chloronitriles are both produced in racemic form because one enantiotopic face of dienophile 16 will participate in a Diels-Alder reaction with the same facility as the other enantiotopic face. In subsequent work, Corey s group demonstrated that racemic hydroxy acid 11, derived in three steps from racemic 14 (see Scheme 3), could be resolved in a classical fashion with (+)-ephe-... 

An extensive review of 4 - - 3-cycloaddition reactions has been presented. The 1,3-difluorooxyallyl intermediate obtained from l-bromo-l,3-difluoropropan-2-one undergoes 4 + 3-cycloaddition with cyclopentadiene and ftiran to give difluorobicyclo[3.2.1]octenones. The use of 4 + 3-cycloaddition reactions of cyclic oxyallyls in the synthesis of natural products has been extensively studied. The intramolecular 4 + 3-cycloaddition of allylic sulfones (111) possessing a diene in the side-chain in the presence of Lewis acids yield cycloadducts (112) in good to excellent yields (Scheme 43). ... 

To extend this methodology, Diels-Alder reactions of several (Z)-4-arylidene (heteroarylidene)-2-phenyl-5(47/)-oxazolones with butadiene, 2,3-dimethylbuta-diene, cyclopentadiene and Danishefsky s diene have been studied. This work demonstrated that the products depended on the nature of the aromatic ring and the diene used. " An interesting application of this methodology is the synthesis of racemic epibatidine 729, a new alkaloid with a 7-azabicyclo[2.2.1]heptane skeleton that has proven to be a very potent analgesic. Preparation of 729 began with the Diels-Alder adduct 726 obtained from (Z)-4-[5 -(2 -chloropyridyhnethylene)]-2-... 

Iron carbonyls also mediate the cycloaddition reaction of allyl equivalents and dienes. In the presence of nonacarbonyldiiron a,a -dihaloketones and 1,3-dienes provide cycloheptenes (Scheme 1.5) [14,15]. Two initial dehalogenation steps afford a reactive oxoallyliron complex which undergoes a thermally allowed concerted [4 + 31-cycloaddition with 1,3-dienes. The 1,3-diene system can be incorporated in cyclic or heterocyclic systems (furans, cyclopentadienes and, less frequently, pyrroles). Noyori and coworkers applied this strategy to natural product synthesis, e.g. a-thujaplicin and P-thujaplicin [14, 16]. 

The indene-derived group. At the Velsicol Chemical Corporation in Chicago in 19 3, Dr. Julius Hyman was seeking new uses for the cyclopentadiene which was a by-product of U.S. synthetic rubber production and was already used by Velsicol for the manufacture of resins and varnishes by the Diels-Alder reaction (6). A literature search revealed Straus s 1930 synthesis of hexachlorocyclopentadiene ( hex ) and, since chlorinated dienes are frequently rather inert, Hyman was interested to determine if hex would participate in the Diels-Alder reaction, either with itself or with cyclopentadiene. 

The latest paper in this field [83] concerns the synthesis of the (S,S)-l,l-bis-ethoxycarbonyl-2,2-bis-p-tolylsulfinylethene (83) and its dienophilic behavior. Reactions with cyclopentadiene occur neither under thermal conditions nor in the presence of Lewis acids, but required the use of high pressure (13 kbar) to afford an 87 13 mixture of 84a and 84b adducts. With acyclic 1-substituted dienes, the combined use of ZnBr2 catalysis and high pressures was required to achieve high yields of cyclohexadienes 84c, resulting from spontaneous pyrolytic desulfinylation of the adducts (Scheme 44). The optical purity of these cyclohexadienes (ee >97%) revealed that both the regioselectivity and diastereo-selectivity of these reactions are complete. 

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