Norbornene, reaction with carbonyl

Substituted norbornane derivatives have been synthesized by the reaction of norbornenes with carbonyl ylides derived from a-diazoketones by a 1,3-dipolar cycloaddition route (Equation 97) <2002TL5981>. These reactions occur in high yields and with excellent o o-selectivity (Table 8). 

The tungsten(II) carbonyl complex (CO)4W(/u.-Cl)3W(SnCl3)(CO)3 has been identified as a very effective catalyst for the hydroarylation of norbornene conducted in arene solution at room temperature. Norbornene adducts with benzene, toluene, p-xylene, and mesitylene have been isolated. On the basis of XH NMR monitoring of several catalytic reactions, a possible mechanism, involving coordination of norbornene to the W(II) atom and its activation, has been proposed.123... 

Electrolysis of benzothiete sulfone 269 yields the phenylmethanesulfinate anion (major) and the o-toluenesulfinate anion (minor).Thermolysis 618,619 gj. photolysis of thiete 1,1-dioxides proceeds via ring-opening to vinyl sulfines, for example. 288, which have been trapped by reaction with water, phenol,methanol, or norbornenes. These intermediates may recyclize to unsaturated sultines (cyclic sulfinate esters) (e.g., 289) or lose sulfur monoxide to give mainly the trans isomers of a,j3-unsaturated carbonyl compounds (e.g., 290). Mass spectra also indicate the formation of unsaturated sultines. ... 

The use of both LIU and HIU has been shown to increase the efficiency of the P-K reaction, which involves the formation of cyclopentenone from the annulation of a cobalt alkynyl carbonyl complex and an alkene. The use of low-power ultrasound, as for example, from a cleaning bath, although capable of producing intramolecular P-K reactions, generated relatively low cyclization yields. The motivation for the use of high intensity came from its ability, as previously described, to effectively decarbonylate metal carbonyl and substituted metal carbonyl complexes. Indeed, HIU produced by a classic horn-type sonicator has been shown to be capable of facile annulation of norbornene and norbornadiene in under 10 min in the presence of a trimethylamine or trimethylamine N-oxidc dihydrate (TMANO) promoter, with the latter promoter producing cleaner product mixtures. This methodology also proved effective in the enhancement of the P-K reaction with less strained alkenes such as 2,5-dihydrofuran and cyclopentene, as well as the less reactive alkenes -fluorostyrene and cycloheptene. The mechanism has been postulated to involve decarbo-nylation of the cobalt carbonyl alkyne, followed by coordination by the amine to the vacant coordination sites on the cobalt. 

Allyl methylcarbonate reacts with norbornene following a ruthenium-catalyzed carbonylative cyclization under carbon monoxide pressure to give cyclopentenone derivatives 12 (Scheme 4).32 Catalyst loading, amine and CO pressure have been optimized to give the cyclopentenone compound in 80% yield and a total control of the stereoselectivity (exo 100%). Aromatic or bidentate amines inhibit the reaction certainly by a too strong interaction with ruthenium. A plausible mechanism is proposed. Stereoselective CM-carboruthenation of norbornene with allyl-ruthenium complex 13 followed by carbon monoxide insertion generates an acylruthenium intermediate 15. Intramolecular carboruthenation and /3-hydride elimination of 16 afford the -olefin 17. Isomerization of the double bond under experimental conditions allows formation of the cyclopentenone derivative 12. 

Several other examples of stereoselective synthesis of polycyclic ketones, via carbonylative [2 + 2 + 1] cycloaddition of organopalladium compounds derived from norbornene and norbor-nadiene, have been reported53,54,121. These reactions are useful in the synthesis of cyclopen-tanoid compounds, such as dihydrojasmone54 The nickel-catalyzed version of this method was used in a total synthesis of methylenomycin B55 and in the stereoselective synthesis of bicy-clo[3.3.0]oct-l-en-3-one derivatives56. Thus, (E)- or (Z)-9-bromo-l-methoxy-7-nonen-2-yne (5), upon intramolecular carbonylative cyclization promoted by tetracarbonyl nickel, afford the same stereoisomer of methyl 1,2,4,5.6,6a-hexahydro-3-methoxymethyl-2-oxo-l-pentaleneac-etate (6) in 43-50% yield with a relative trans configuration of the H-l and H-6a protons. 

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). 

In 2010, Buchmeiser [56] developed a similar system that capitalized on the thermally reversible carboxylation [11] of NHCs (Scheme 31.13, inset). By employing the NHC-CO2 adduct (which essentially is a protected NHC), the reaction conditions did not have to be stringently air- and moisture-free to prevent NHC decomposition. Synthesis of the norbornene-functionalized monomer 37 allowed the molybdenum-catalyzed ROMP with l,4,4a,5,8,8a-hexahydro-l,4,5,8-exo-ewdo-dimethanonaphthalene (a ditopic norbornene) to produce crossHnked polymer 38 with pendant CO2-masked NHCs (Scheme 31.13). Upon heating in the presence of Rh, Ir, or Pd species, the NHC-metal-functionalized polymers 39 were formed and found to contain >20mol% metal, as determined with inductively coupled plasma optical emission spectrometry (ICP-OES). The C02-masked NHC material was found to catalyze the carboxylation of carbonyl compounds and the trimerization of isocyanates upon thermal deprotection (i.e., decarboxylation). Moreover, the NHC-metal-crosslinked materials were found to catalyze Heck reactions, transfer hydrogenations, and also the polymerization of phenylacetylene (M = 8.4 kDa, PDI = 2.45, as determined with GPC in DMF against PS standards). This modular system provides an array of options for catalysis from simple modifications of polymer-supported, C02-masked NHCs. 

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