Norbornadiene synthesis

The reaction of o-iodophenol, norbornadiene and CO proceeds via alkene and CO insertions to afford the lactone 562, which is converted into coumarin (563) by the retro-Diels-Alder reaction. In this coumarin synthesis, norbona-diene behaves as a masked acetylene[4)3],... 

The /lomo-Diels-Alder reaction is a [2 + 2 + 2] cycloaddition of a 1,4-diene with a dienophile which produces two new bonds and a cyclopropane ring. This reaction is an example of a multi-ring-forming reaction that to date has found few applications in synthesis, since the use of 1,4-dienes has been limited mainly to bridged cyclohexa-1,4-dienes and almost exclusively to norbornadiene. Lewis-acid catalysts accelerate /lowo-Diels-Alder reactions and increase the selectivity for the [2 + 2 + 2] vs. [2 + 2] cycloaddition. 

This route provides a convenient method for synthesizing deltacyclenes 89 which have been proven to be useful in the synthesis of highly strained unnatural products of theoretical interest [88]. Diels-Alder reactions of norbornadiene (88) have been successfully activated by a nickel catalyst [89] (Scheme 3.17). Amarked influence of the catalyst on the endo-exo diastereoselectivity has been observed. 

Novel chiral. separations using enzymes and chiral surfactants as carriers have been realized using facilitated transport membranes. Japanese workers have reported the synthesis of a novel norbornadiene polymeric membrane with optically active pendent groups that show enantio.selectivity, which has shown promi.se in the. separation of propronalol. 

When irradiated in the presence of norbornadiene and high-pressure synthesis gas, rhodium chloride is converted to a catalyst which is active for a variety of reactions. /2A/. The salt is probably converted photochemically to the rhodium norbornadiene complex 9. This dimer may undergo a consecutive photoreaction to give the monomeric hydrido complex 10, which is the actual catalyst for polymerisation, hydrogenation, and hydroformylation reactions. 

Bicyclo[2.2.1]hepten-7-one is a useful intermediate in the synthesis of a variety of norbornane derivatives. The present procedure involves a four-step synthesis from hexachlorocyclo-pentadiene with a 39% overall yield. The next best method3 involves a four-step synthesis from norbornadiene with a 15% overall yield. 

The incorporation of sulphonyl groups does not inhibit the cyclization process as demonstrated by Gleiter and Ohlbach133, who have reported the efficient synthesis of the quadricyclane 252 by irradiation of the norbornadiene derivatives 253. A study has also been made of the sulphonyl-substituted norbornadiene derivatives 254134 135. 

In 1991, Park reported123 the first synthesis of iron alkynylcarbene complexes (184), involving the nucleophilic attack of a lithium acetylide on pentacarbonyl iron, followed by electrophilic quench. With such compounds in hand, he proceeded to investigate their reactivity123,124 and found that upon addition of cyclopentadiene to the alkynylcarbene complexes 184, the products formed were 774-vinylketene complexes (185). During column chromatography, some of these products (185.a and 185.b) were transformed into the tricarbonyl(norbornadiene)iron derivatives 186. Others (185.C and 185.d, not shown) were hydrolyzed as part of the workup procedure, to afford pure samples of the norbornadiene complexes 186.C and... 

Olah and co-workers reported the synthesis of 2,2,5,5-tetranitronorbornane (127) from 2,5-norbornadiene (122). In this synthesis formylation of (122) with formic acid yields the diformate ester (123), which on treatment with chrominm trioxide in acetone yields 2,5-norbomadione (124). Formation of the dioxime (125) from 2,5-norbornadione (124) is followed by direct oxidation to 2,5-dinitronorbomane (126) with peroxytriflnoroacetic acid generated in situ from the reaction of 90 % hydrogen peroxide with TFAA. Oxidative nitration of 2,5-dinitronorbornane (126) with sodium nitrite and potassium ferricyanide in alkaline solution generates 2,2,5,5-tetranitronorbornane (127) in excellent yield. 

The most common alkenes employed in the Pd-catalysed synthesis of alternating polyketones are ethene, styrene, propene and cyclic alkenes such as norbomene and norbornadiene. Even though the mechanism does not vary substantially with the alkene, the reactions of the various co-monomers are here reported and commented on separately, starting with the ethene/CO copolymerisation, which is still the most studied process. As a general scheme, the proposed catalytic cycles are presented first, then the spectroscopic experiments that have allowed one to elucidate each single mechanistic step. 

The most successful and widely used synthesis of higher substituted derivatives of M(CO)6 (M = Cr, Mo, W) is via the thermal displacement of mono- or polyhapto ligands from the appropriate carbonyl complex. Thus, from C7HgM(CO)4 (M = Cr, Mo, W C7H8 = norbornadiene, cyclohepta-... 

Special iodonium salts. A range of o-trimethylsilyl-phenyliodonioarenes [111] and heteroarenes [112] as well as some similar Wc-compounds coming from norbornadiene [113] and o-carborane [114] have been obtained from the corresponding bis trimethylsilyl precursors upon reaction with one equivalent of (diacetoxyiodo)benzene. These compounds are useful for their facile in situ conversion into benzyne-type intermediates for benzyne itself the whole procedure is available in Organic Syntheses [115]. A recent improvement involved the synthesis of a new benzyne precursor illustrated in Scheme 38 [116]. 

Nickel catalysts for the syntheses of cyclic compounds were first successfully utilized by Reppe, who was able to prepare cyclooctatetraene from acetylene (65). This eight-membered ring synthesis, and also the preparation of cyclic products from strained olefins (e.g., bicycloheptene and norbornadiene) and acrylonitrile, have been adequately reviewed elsewhere (7) and will therefore not be considered further. A short account of the cyclization reactions of butadiene using nickel-containing catalysts has appeared previously in this series (/). The discovery of new synthetic possibilities and a deeper understanding of the mechanism of these reactions justify a more extensive treatment. 

A new synthesis of isoxazoles is by successive treatment of a ketoxime with butyllithi-um, the ester of a carboxylic acid and sulfuric acid, e.g. 1 -> 2 (94S989). Hitrovinyl oximes 3 (R1, R3 = alkyl or aryl) undergo oxidative cyclization to isoxazoles 4 by the action of DDQ or iodine/potassium iodide (94JHC861). Flash-vacuum pyrolysis of the 1,3-dipolar cycloadduct 5 of acrylonitrile oxide to norbornadiene results in a retro-Diels-Alder reaction to give cyclopentadiene and 3-vinylisoxazole 6 (94CC2661). 

Zyk et al. <2000RJ0794> reported the synthesis of fused-ring thietanes by the reaction of the bis-morpholine sulfide-phosphoryl trihalide complex 85 with norbornadiene. The formation of 4-thiatricyclo[3.2.1.03,6]octane 86 was demonstrated and yields varied slightly depending on the phosphoryl trihalide used. When phosphoryl trichloride was used, the yield was 69% in the case of phosphoryl tribromide, it was 72%. The complex 84 was obtained by the reaction of the bis-morpholine sulfide with phosphoryl trihalide in dichloromethane at —40°C (Scheme 15). The same authors <1996RCB2393> performed a similar reaction of norbornadiene with bis-morpholine disulfide-phos-phoryl tribromide complex 87, which led to the formation of the same thietane 86 in 63% yield (Scheme 15). These reactions have also been described by Robin and Rousseau in a review <2002EJ03099>. 

In addition to the conventional McBride synthesis using simple alkenes, a few other unsaturated substrates serve as starting materials for the construction of phosphetane rings. For example, the reaction of norbornadiene with chlorophosphines (ClP(OEt)2), instead of dichlorophosphines, afforded tetracyclic phosphetane oxides (Equation 23) <1996JHC979>. 

One of the first examples of ruthenium-catalyzed C-C bond formation afforded the synthesis of cyclobutenes, from norbornene derivatives with dimethyl acetylenedicarboxylate, and was reported by Mitsudo and coworkers [45, 46] by using various catalysts such as RuH2(CO)[P(p-C6H4F)3]3 or RuH2(PPh3)4. More recently, the complex Cp RuCl(COD) has shown to be an excellent catalyst for the [2+2] cycloaddition of norbornenes with various internal alkynes [45] (Eq. 33) and with a variety of substituted norbornenes and norbornadienes [47]. The ruthenacycle intermediate, formed by oxidative coupling, cannot undergo /1-hydride elimination and leads to cyclobutene via a reductive elimination. 

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