Dienic products

Bicyclic dienic products recently synthesized by this method (Scheme 36) are lactams 144a and b (07T8267) and enamine ester 145 (09CEJ4565). The precursor of the latter substance originates from a four-component synthesis followed by y-allylation. The alternative y-propargylation and subsequent ring-closing enyne metathesis performed under an ethene atmosphere lead to the 8-vinyl derivative of product 145. 

In a very recent experimental study [32], dimerization of cyclopropene was found to yield a dienic product with two three-membered rings, that could be... 

Fe—Fe bond can be assigned structures 201 or 202 based on spectral data. The other product of this reaction is 193 (R = r-Bu), however, it is produced in minor amounts. Complexes 199 (R = R = r-Bu, R = Ph, R = r-Bu) were obtained. Reaction of 146 (M = Mo, R = Ph, R = R = Ft, R = r" = Me) with (benzyli-deneacetone)iron carbonyl gives rise to the bimetallic complex 200 (M = Mo), which reacts further with the free phosphole to form the bimetallic heteronuclear sandwich 203. The preferable coordination of the molybdenum atom to the dienic system of the second phosphole nucleus is rather unusual. The molybdenum atom is believed to have a greater tendency to coordinate via the trivalent phosphorus atom than via the dienic system. 

In the UV spectrum of the protonation products there is a hypsochromic shift of the absorption maximum of enyne system compared to the bases (74DIS) this agrees with the data of the protonation of simple enamines and dienic amines (69MI1). 

Witli tlie reagent PbCu in tlie presence of tlie additives BF and PBu- , ees of up to 9 596 were obtained, wb de values of up to 8 596 were acliievable witli a vinyl copper reagent. Chiral dienic acetals have also been studied tliree regioisomeric products could be obtained in tliis case as tlie result of Su2, Su2, or Su2" attaclt of tlie organocopper reagent [25]. Mixtures were indeed obtained witli alKyl copper reagents, but PbCu-BF resulted in fotniation of only tlie S 2 and Su2" products, witli selectivity for tlie latter fSclieme 8.12). 

Huisgen has reported in 1963 about a systematic treatment of the 1,3-dipolar cycloaddition reaction as a general principle for the construction of five-membered heterocycles. This reaction is the addition of a 1,3-dipolar species 1 to a multiple bond, e. g. a double bond 2 the resulting product is a heterocyclic compound 3. The 1,3-dipolar species can consist of carbon, nitrogen and oxygen atoms (seldom sulfur) in various combinations, and has four non-dienic r-electrons. The 1,3-dipolar cycloaddition is thus An +2n cycloaddition reaction, as is the Diels-Alder reaction. 

Intramolecular Diels-Alder reactions employing furan as the diene component are an effective step in the synthesis of many natural products, but difficulties are sometimes encountered due to the poor dienic character of the aromatic ring. Using CDs can help to overcome this problem. Thus, when 73 is heated in water at 89 °C for only 6h a 20% epimeric 1 2 mixture of 74 and 75 is... 

Cycloalkenones and/or their derivatives can also behave as dienic partners in the Diels-Alder cycloaddition. It is well documented [41] that cyclic acetals, for example, can interconvert with ring-opened enol ether forms, in a reversible manner the latter compounds can then be trapped by various dienophiles. Thus dienes 119 and 120 reacted with [60]-fullerene (Ceo) at high pressure, affording highly thermally stable products [42] (Scheme 5.16). Ketones 123 and 124 could be directly obtained by cycloaddition of enol forms 121 and 122 of 2-cyclopen-ten-and 2-cyclohexen-l-one, respectively. 

Harano and colleagues [48] found that the reactivity of the Diels-Alder reaction of cyclopentadienones with unactivated olefins is enhanced in phenolic solvents. Scheme 6.28 gives some examples of the cycloadditions of 2,5-bis-(methoxycar-bonyl)-3,4-diphenylcyclopentadienone 45 with styrene and cyclohexene in p-chlorophenol (PCP). Notice the result of the cycloaddition of cyclohexene which is known to be a very unreactive dienophile in PCP at 80 °C the reaction works, while no Diels-Alder adduct was obtained in benzene. PCP also favors the decarbonylation of the adduct, generating a new conjugated dienic system, and therefore a subsequent Diels-Alder reaction is possible. Thus, the thermolysis at 170 °C for 10 h of Diels-Alder adduct 47, which comes from the cycloaddition of 45 with 1,5-octadiene 46 (Scheme 6.29), gives the multiple Diels-Alder adduct 49 via decarbonylated adduct 48. In PCP, the reaction occurs at a temperature about 50 °C lower than when performed without solvent, and product 49 is obtained by a one-pot procedure in good yield. 

The reaction in Eq. 39 lo > is really quite easy to understand, although the result seems geometrically impossible if a molecular model is examined. The reaction involves an yn-n state since dienic quenchers are noneffective, and the stereochemistry of the product is well-established. 103> The reaction diagram, Fig. 9, provides the key to under-... 

The reactions of free radicals with furan and its derivatives can give both addition and substitution products depending on the specific system (11-13). With 2-substituted furans, the attack takes place predominantly at C5 and leads, by additon, to the corresponding furyl radicals which must be viewed as relatively stabilized interemediates because of the dienic-aromatic character of the furan heterocycle. These premises are essential to the understanding of the varied responses of furan monomers to free-radical activation. 

The first work was carried out by radiochemical polymerization of a mixture of dienic and acrylic monomers on a PVC latex. A parallel study by chemical means leads to equivalent products and the development of a reinforcing resin which satisfied the requirements listed above. At present a resin of this type is manufactured and sold by Pechiney-Saint Gobain under the name Lucovyl H 4010 (10). 

Asymmetric induction in cyclizution of a dienic acetal. Johnson et al reported a very high degree of asymmetric induction in the SnCl4-catalyzed cyclization of the iiL ctal I, derived from (—)-2,3-butanediol. Cyclization results in two axial ethers and two equatorial ethers cleavage and Jones oxidation converts these products into an nctuionc mixture consisting of 2a and 2b in the ratio 8 92. 

Fabian examined the geometries of the possible cycloaddition products between ketenimine and acrolein as well as of the respective transition states by ab initio calculations at the MP2/6-31G level <1997JA4253>. Two of the 12 possible products of [4+2] and [2+2] cycloaddition are oxazetidines 3 and 4 (Scheme 1). With respect to the site selectivity of the heterodiene, the [2+2] products resulting from the addition of the ketenimine onto the dienic C=C... 

Tripincer template-directed cyclization of a dienic pyridine precursor leads to the formation of the 69-membered ring trimeric heterocycle 112 (Figure 2.6). Decomplexation of the tripincer from the product is realized with NaCl [72]. The synthesis of a [2]rotaxane by M-RCM using a similar pincer-pyridine complex for pre-assembly was also reported by Leigh et al. [73]. 

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