Norbornene analogs

Confirmation that the polymerizations proceed via metallacyclic intermediates was obtained by studying the ROMP of functionalized 7-oxanorbornadienes. These polymerize slower than their norbornene analogs, allowing NMR identification of the metallacyclobutane resonances and subsequent monitoring of ring opening to the first insertion product. In addition, the X-ray crystallographic structure of complex (212) has been reported.533... 

In a manner analogous to classic nitrile iinines, the additions of trifluoro-methylacetonitrile phenylimine occur regiospecifically with activated terminal alkenes but less selectively with alkynes [39], The nitnle imine reacts with both dimethyl fumarate and dimethyl maleate m moderate yields to give exclusively the trans product, presumably via epimenzation of the labile H at position 4 [40] (equation 42) The nitrile imine exhibits exo selectivities in its reactions with norbornene and norbornadiene, which are similar to those seen for the nitrile oxide [37], and even greater reactivity with enolates than that of the nitnle oxide [38, 41], Reactions of trifluoroacetomtrile phenyl imine with isocyanates, isothiocyanates, and carbodiimides are also reported [42]... 

Formation of mixtures of products in these reactions can be attributed largely to the properties of the acetate group. The reactions of a number of cycloalkenes with thallium(III) salts have been investigated in some detail and the results obtained have served both to elucidate the stereochemistry of oxythallation and to underline the important role assumed by the anion of the metal salt in these oxidations. The most unambiguous evidence as to the stereochemistry of oxythallation comes from studies by Winstein on the oxythallation of norbornene (VII) and norbornadiene (VIII) with thal-lium(III) acetate in chloroform, in which the adducts (IX) and (X) could be precipitated from the reaction mixture by addition of pentane 128) (Scheme 11). Both by chemical means and by analogy with the oxymercuration... 

Phosphite complexes of platinum(0) have received substantially less attention than have phosphine complexes.44 [Pt P(OC6H4OMe-2)3 3] can be prepared by reduction of the [PtCl2 P-(OC6H4OMe-2)3 2] complex in the presence of the phosphite or by the reaction of the phosphite with Lris(//2-norbornene)platinum(II) 44 Alkene complexes of bis(phosphite)platinum(II) can be prepared in a similar manner to the analogous phosphine complexes. 

The addition of thiobenzoyl isocyanate to norbornene and norbornadiene resulted in the thiazinones 230 (R = Ph) and 231, respectively (67CB685). The ter/-butyl- and mesityl-substituted analogs of 230 were prepared by the same method. In the case of a benzyl substituent, the derivative 232 containing an exo double bond was formed (81CB549). 

Analogous methyl azidoformate forms with norbornene a thermal unstable triazoline.251 The decomposition products are 40% aziridine and 55% imide. Furthermore it has been observed that the rate of nitrogen evolution of the triazoline from methyl azidoformate increases threefold when triglyme and 20-fold when dimethyl sulfoxide are substituted for 1,1-diphenylethane as solvents. This fact supports a betaine intermediate in the thermal decomposition reaction. The triazoline from 2,4-dinitrophenyl azide and norbornene could just be isolated, but from picryl azide only the aziridine was obtained.252-254 Nevertheless, the high negative value of the activation entropy (—33.4 eu) indicates a similar cyclic transition state for both reactions. 

The thermolysis of triazoline adducts from other polycyclic bridgehead olefins is analogous to that of the norbornene-azide adducts (Scheme 164) and affords a route for the synthesis of various aziridine ring sys-... 

The resulting complex 10 can be viewed as the product of an insertion equilibrium analogous to that leading from 2 to 4 (Scheme 1). This time, however, the presence of the two ortho substituents shifts the equilibrium to the left and norbornene is expelled with formation of the o-dialkylated arylpalladium halide species 11. This lends itself to a variety of reactions enabling the formation of organic products and palladium(O), which can be represented schematically as follows (Scheme 4). 

Analogously to ethylene-carbon monoxide copolymers, alternating copolymers between cycloolefins such as norbornene and carbon monoxide have been synthesised using cationic Pd(II) complexes modified by phosphorus ligands such as [Pd(MeCN)n(PPh)4 J[BF4]2( = 1,2,3) [27]. General requirements for the... 

Analogously to the titanacycle catalyst, similar trisubstituted tantallacyclo-butanes were prepared, but with the use of tantalum alkylidene for the reaction with norbornene [100-102] ... 

Earlier, a one-pot procedure based on consecutive Pd-catalyzed aryl-aryl coupling followed by N-C bond formation had been described for the synthesis of phenanthridones and their thiophene analogs <2004OL4759>. The starting materials were 2-iodotoluene and 3-bromothiophene-2-carboxamides or 3-bromobenzo[3]thiophene-2-carboxamides (Equations 40 and 41). The conditions were rather critical in order to prevent the nucleophilic amide group from coordinating with the palladium, tri-2-furylphosphine had to be added to the reaction mixture. Norbornene serves to form a palladacycle which then reacts with the bromoamide. 

Analogously, rearrangements could not be suppressed in reactions with methylenecyclopropane, vinylcyclopropane or norbornene (Scheme 28). The intermediate carbocations 35-37 are not intercepted, and the rearranged products 38-40 have been isolated instead [106-108],... 

The few available data for carbocation additions to cycloalkenes (Scheme 41) show an analogous reactivity order Cyclopentenes are more reactive than the acyclic analogs, and the only cyclohexene derivative shown in Scheme 41 is less reactive. Because of the paucity of data, this analogy should not be overinterpreted. The location of norbornene between the compounds which give secondary and tertiary carbocations has already been mentioned (Scheme 36 in Section III.D.4.a.). 

The norbomene complex [Li(tmeda)]2Ni(norbornene)2 (64) (89) is analogous to 62 and 63 in having a tetrahedral arrangement of carbon atoms and donor atoms around the lithium, but the geometry of the complex necessarily brings the lithium atom into close contact with the transition metal atom. 

The diastereoselective addition of aniline to norbornene was accomplished using a catalytic amount of iridium(I). As the intermediate azametallacyclobutane 2 could be isolated its stereochemistry was determined by X-ray analysis both iridium and nitrogen occupy the exo position41. However, the scope of the amination method, with respect to the nature of the amine and the structure of the alkene, was not determined. Conversely, the analogous rhodium(I)-cat-alyzed reactions of norbornene and aromatic amines gave mixtures of hydroamination and hydroarylation products106. 

New and efficient procedures for the direct episulfidation of alkenes have been developed. Addition of triphe-nylmethylthiosulfenyl chloride to cyclopentene leads to the adduct 88, which by reduction of the disulfide with LiAlH4 give episulfide 87 in high yield (Scheme 48) <2000SUL131, 1998JOC8654>. The analogous reaction with norbornene yields the jco-episulfide 89 in a diastereoselective fashion. 

An analogous sulfur transfer with methylthiirane as sulfur source and Rh2(OAc>4 as catalyst converts norbornene and norbornadiene to their episulfides in a so-called thiirane metathesis <1998SL391>. In the same paper, examples of the SO transfer from thiirane A-oxide (97, an episulfoxide) to norbornene and norbornadiene have been described. In both cases, two diastereomers of type 98a and 98b are obtained, both with an o-oriented episulfoxide structure (Scheme 54). 

---