Norbornenes 2 + 2 + 2 cycloaddition reactions

The study of high pressure cycloaddition reactions of tropone (125) with maleic anhydride and norbornene allowed the reaction activation volumes to be measured and showed that they are large, negative and solvent-dependent (Scheme 5.17) [43a]. 

Itoh and coworkers111 carried out tandem [2 + 2 + 2]/[4 + 2] cycloadditions catalyzed by a ruthenium catalyst. The reaction of diyne 147 with excess norbomene 148 in the presence of ruthenium catalyst 153, for example, afforded 149. Adduct 150 either dissociated from the catalyst or reacted with another equivalent of norbornene. In the latter case, a ruthenium catalyzed Diels-Alder reaction occurred, affording hexacyclic adduct 152 via 151 (equation 43). Compounds 150 and 152 were obtained in yields of 78% and 10%, respectively. Both cycloaddition reactions proceeded with complete stereoselectivity. When 1,6-heptadiyne was used instead of 147, only trace amounts of a cycloadduct were obtained. Replacing norbornene by norbornadiene, which was expected to result in polymer formation, did not afford any adduct at all. 

An interesting preparation of aliphatic diazoalkanes (R R C = N2 R, R = alkyl) involves the photolysis of 2-alkoxy-2,5-dihydro-1,3.4-oxadiazoles (see Scheme 8.49). When the photolysis is carried out in the presence of an appropriate dipolarophUe, the diazo compounds can be intercepted (prior to their further photolysis) by a [3 + 2] cycloaddition reaction (54). As an example, 2-diazopropane was intercepted with A-phenylmaleimide (54) and norbornenes (55) to give the corresponding A -pyrazolines. 

Little regioselectivity is observed in these cycloaddition reactions. The evidence of strain being a factor in these cycloadditions is seen from the relative inertness of norbornene (30) and m-l-methylcyclooctene to such cycloadditions. 

The meso-ionic l,3-dithiol-4-ones (134) participate464-77 91-93,94 in 1,3-dipolar cycloaddition reactions giving adducts of the general type 136. They show a remarkable degree of reactivity toward simple alkenes94 including tetramethylethylene, cydopentene, norbornene, and norbor-nadiene as well as toward the more reactive 1,3-dipolarophilic olefins dimethyl maleate, dimethyl fumarate, methyl cinnamate, diben-zoylethylene, JV-phenylmaleimide, and acenaphthylene. Alkynes91-93 such as dimethyl acetylenedicarboxylate also add to meso-ionic 1,3-dithiol-4-ones (134), but the intermediate cycloadducts are not isolable they eliminate carbonyl sulfide and yield thiophenes (137) directly.91-93... 

DFT and ab initio studies of the cycloaddition reaction between methyleneketene and cyclopentadiene indicated that the norbornene adduct is the primary reaction product from a 1,2-addition.131 The thermal 4 + 2-cycloaddition of o-xylylenes (104) with /3-nitro-me.S 0-tetraphenylporphyrin (103) produced a high yield of the chlorin (105) together with low yields of the naphthoporphyrin (106) and the bis-naphthoporphyrin... 

The dithionitronium cation SNS+ (as the AsFg salt) underwent quantitative concerted symmetry-allowed cycloaddition reactions with alkenes (ethylene, methylethylene, trans- and +r-l,2-dimethylethylene, 1,1-dimethyl-ethylene, tetramethylethylene, and norbornene) to give 1,3,2-dithiazolidine cations 76 (Equation 20) <1996JCD1997>. 

Among the carbonylative cycloaddition reactions, the Pauson-Khand (P-K) reaction, in which an alkyne, an alkene, and carbon monoxide are condensed in a formal [2+2+1] cycloaddition to form cyclopentenones, has attracted considerable attention [3]. Significant progress in this reaction has been made in this decade. In the past, a stoichiometric amount of Co2(CO)8 was used as the source of CO. Various additive promoters, such as amines, amine N-oxides, phosphanes, ethers, and sulfides, have been developed thus far for a stoichiometric P-K reaction to proceed under milder reaction conditions. Other transition-metal carbonyl complexes, such as Fe(CO)4(acetone), W(CO)5(tetrahydrofuran), W(CO)5F, Cp2Mo2(CO)4, where Cp is cyclopentadienyl, and Mo(CO)6, are also used as the source of CO in place of Co2(CO)8. There has been significant interest in developing catalytic variants of the P-K reaction. Rautenstrauch et al. [4] reported the first catalytic P-K reaction in which alkenes are limited to reactive alkenes, such as ethylene and norbornene. Since 1994 when Jeong et al. [5] reported the first catalytic intramolecular P-K reaction, most attention has been focused on the modification of the cobalt catalytic system [3]. Recently, other transition-metal complexes, such as Ti [6], Rh [7], and Ir complexes [8], have been found to be active for intramolecular P-K reactions. 

The vast majority of bicyclic phosphole derivatives with norbornene- and norbornadiene-derived skeletons are prepared via classical [4+2] cycloaddition reactions of phospholes. While Diels-Alder reactions of phospholes with CN 4 (e.g., oxides and sulfides) are common through direct reaction with dienophiles, this type of reaction is comparatively rare for CN 3 phospholes (see Section 3.15.5.1.4). 

Using a similar approach, through [2+3] dipolar cycloaddition reactions, the syntheses of 532 and 533 were accomplished from thiocarbonyl y-imides 531 and norbornene-3,4-dicarboxylate or /ra r-cycloctene <2000T4231>. 

CEJ4035>. Diastereospecific synthesis of r-/3-lactams can be effected via cycloaddition reaction of bisimines and the ketene derived from 582 (R = CH2CO2H) (Staudinger reaction) <2000T8555>. Ruthenium-catalyzed [2-1-2] cycloaddition of norbornene and ynamide 582 (R = C=CPh) <2006T3823> was reported. 

The cycloaddition reaction of the adduct 575, obtained from -Bu3P and CS2, to a strained double bond such as in norbornene, gave the stable zwitterionic product 576. The latter dissociated to yield 577, which could be trapped with aldehydes in a Wittig reaction to give the tricyclic alkylidenedithiolanes 578 (Scheme 81). The compound 575 also reacted with acetylenic dipolarophiles to give dihydro-TTF derivatives <1996PS593, 1997T10441>. 

Under refluxing conditions, 1,4-benzothiazines 82 undergo a cycloaddition reaction with dimethyl acetylenedicarboxylate (DMAD) to afford 1,4-benzodithiin 83 (Equation 15) <1982CC612>. Similarly, heating 1,4,2-dithiazine 84 in the presence of norbornene 85 produced 1,4-dithiine 86 (Equation 16) <1997JP11157, 2000JHC955>. 1,3-Dipolar cycloadditions of 1,2,3-oxathiazines with 1,3-diphenylnitrilimine were described in CHEC-II(1996) <19%CHEC-II(6)825>. 

A series of [2.2.1]bicycloheptenyl (norbornene) functional prepol)nners have been prepared via the cycloaddition reaction of cyclopentadiene monomer with corresponding acrylics. When these materials are formulated with an appropriate multifuntional thiol crosslinker and photoinitiator and irradiated, a rapid, exothermic, crosslinking reaction takes place. When the acrylic precursors are organic resins, the derived polymers behave like toughened plastics. The choice of a norbornene functional polydimethylsiloxane precursors gives elastomeric products. 

An efficient protocol for the synthesis of syn-facially bridged norbornane frameworks has been developed via the tandem cyclization-cycloaddition reactions of the carbonyl ylide 57 with norbornene derivatives. The reaction of the diazo ketone 56 with the dipolarophile 62 in the presence of Rh2(OAc)4 furnished [85] the 5y -facially bridged oxa-norbornane framework 63 in high yield (Scheme 17). 

Maleic anhydride was used as the dienophile, allowing for further functionalization following the assembly of the norbornene skeleton. Diels-Alder cycloadditions of the above-mentioned fiilvene derivatives with maleic anhydride at elevated temperatures, between 80 °C and 120 °C, and moderate concentrations, 0.2 to 0.5 M, afforded quantitative yields of the corresponding norbornene derivatives 5, 7, and anhydride precursor of 9 (see Table I) (29). At total adduct concentrations above 1.5 M or temperatures above 130 °C, a solid oligomeric side product, presumably a copolymer of the reactants, was obtained. Two isomers, endo or exo, can be obtained from cycloaddition reactions, depending on the nature of adducts or the reaction temperature. These isomers exhibit different polymerization kinetics, where, in most cases, endo adducts polymerize very slowly, and result in low conversions. 

Fig. 1 Cycloaddition reactions employed in nucleic acid labeling with reporter groups (green star). A Cu -mediated azide-alkyne cycloaddition (CuAAC) of a terminal alkyne with an azide. B Strain-promoted azide-alkyne cycloaddition (SPAAC) of an azide with a cyclooctyne derivative. C Staudinger ligation of an azide with a phosphine derivative (not a cycloaddition reaction, see below). D Norbornene cycloaddition of a nitrile oxide as 1,3-dipole and a norbornene as dipolarophile. E Inverse electron-demand Diels- Alder cycloaddition reaction between a strained double bond (norbornene) and a tetrazine derivative. F Photo-cUck reaction of a push-pull-substituted diaiyltetrazole with an activated double bond (maleimide)...

Figure 1.15 Modern variants of the Diels-Alder cycloaddition reaction (a) Inverse-electron-demand Diels-Alder (lEDA) reaction between tetrazine and norbornene/ and (b) hetero Diels-Alder (HDA) reaction between thiocarbonyl and cyclopentadiene. ...

Vinylsulflnes 38 (R = PhCH=CH-) can also participate as dienes in the [4+2] cycloaddition reaction with norbornene to give the tricyclic adduct 41 in 90 % yield. 

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