Nucleophilicity 2£,6£ -Octa-2,6-diene

These results have been interpreted in terms of trans addition of mercuric ion and nucleophile where the attack of the mercuric ion takes place from the more hindered side of the diene molecule. A transition state 197, involving an endo attack of mercuric ion with some stabilization by coordination to the 8,9-ethylenic bond to the mercury atom, has been proposed to support the suggested mechanism. Analogously, and in sharp contrast to the results obtained167 in the mercuration of norbomadiene which reacts with mercury salts via the usual scheme of exo-syn addition, the principal pathway in the mercuration of bicyclo[2.2.2]octa-2,5-diene is the formation of endo-syn products (equation 165). 

Comparison with the reported reactivity of the spiro[2.5]octa-l,4-dien-3-one 110 and 4-(hexafluoroisopropylidene)cyclohexa-2,4-dien-l-one 111 have suggested that the conjugated cyclopropane ring of compounds 108 and 109 imparts a strong acid dependence to its reactivity with nucleophiles, Eq. (45). This property is likely to be relevant for the exceptional reactivity of these antibiotics toward DNA [148]. 

Soft nucleophiles or halide ions may also coordinate to C to give [Pd(l, 2,3-r)3-octa-2,7-dien-l-yl)(X)(L)] (F) (X = Nu, Cl ), which is known to be less active [47] and may even lead to catalyst deactivation. Finally, the by-product 1,3,7-octatriene can also be formed from intermediate C, by proton abstraction at the 4-position of the r 3,r l-octadienyl ligand. Note that the proton that is lost upon 1,3,7-octatriene formation is different from the proton added by the nucleophile (4 position vs. 6 position, respectively), which points at the general irreversibility of the step going from B to C. 

A serendipitous discovery(6) that [Pt(cod)2] (cod cyclo-octa-1,5-diene) reacted with perfluoropropene to give the diplatinum complex [pt2 y-C(CF3)2 (cod)2], rather than the simple Ti2 adduct [Pt(CF2 CFCF3)(cod)], led to the idea(7) that mononuclear metal-carbene or -carbyne complexes would combine with nucleophilic and co-ordinatively unsaturated metal species (M") ... 

Photolysis of bicyclo[3.2.2]octa-3,6-dien-2-one derivatives, for example the adduct of tropone with benzyne 33 a in water gave the three-membered ring derivative 35 a, while photolysis in acetonitrile gave the cyclopentanone derivative 37 a which must arise from the 1,3-shift product 36a.This different behavior in these two solvents was rationalized in the following way the efficient [3,3] shift of 33 a to cyclopropyl ketene 34 a is thermally reversible, so that in the absence of a nucleophile 35a is not observed. In that case, the less efficient 1,3-shift to form 36a and then 37a is the only detectable reaction. The ketene 34a was detected as the major product of photolysis of adduct 33 a at low temperature methanolysis of 34 a at — 80 "C gave only the enfifo-configurated ester 35 a. 

In a study towards the synthesis of the tricarbonyliron complex of 8-methylenespiro[2.5]octa-4,6-diene 52 starting from spiro[2.5]octa-4,6-diene (49), conversion of its tricarbonyliron complex 50 via hydride abstraction, nucleophilic addition of hydroxide and oxidation gave the spiro[2.5]octa-5,7-dien-4-one-tricarbonyliron complex 51, which, however, could not be converted to the target complex 52 via Wittig olefination. An alternative approach to generate a Wittig reagent from spiro[2.5]octa-4,6-diene (49) via conversion to a phosphonium system 53 was likewise unsuccessful. ... 

Upon decomplexation, using various methods, cyclopropane products are obtained (see Section 5.2.6.1.1). As an example, synthesis of homotropone (9 bicyclo[5.1.0]octa-3,5-dien-2-one) is achieved starting from cyclooctatetraenetricarbonyliron complex via protonation, formation of the bicylo[5.1.0]octadienylium cation complex 8, nucleophilic addition of sodium hydroxide and oxidative decomplexation. ... 

Other carbenes which exhibit nucleophilic behavior include benzocyclo-butenylidene (13), [49] bicyclo[3.2.1]octa-2,6-dien-4-ylidene (14), [50] and bicyclo [3.2.1]octa-2-en-4-ylidene (15), [50] with reported p values (vs. a) of +1.57, +0.25, and +0.68, respectively. In all cases, computations suggest either an excess of negative charge on the carbenic center or a high-lying HOMO (essentially the carbene lone pair), which account for the carbenes nucleophilicity toward styrenes. 

Thus, the degree of manifestation of n-participation in reactions with a nucleophile changes essentially depends on its strength. The 2,3-tetrafluorobenzo-bicyclo[2,2,2)octa-2,7-diene skeleton is thermodynamically less stable than the... 

Treatment of 5,8-bis(trimethylsilyl)cyclo-octa-l,3,6-triene or 3,5,8-tris(trimethyl-silyl)cyclo-octa-l,3,6-triene with triruthenium dodecacarbonyl gave the pentalene complexes (352 X = H or SiMe ). Tricarbonyl(Ti-cyclo-octa-l,5-diene)ruthenium and tricarbonyl(T)-cyclo-octa-l,3-diene)osmium have been prepared. They react with trityl fluoroborate to give cyclo-octadienylium complexes [(CgHn)M(CO)3] which react with anionic nucleophiles to give neutral compounds, some of which... 

The use of (acylamino)malonate as a nucleophilic reagent toward 1,3-dienes is an efficient route for the synthesis of a-amino acid derivatives. The reaction of diethyl acetamidomalonate 15 with butadiene in the presence of Pd(OAc)2-PPh3-NaOPh as a catalyst produces diethyl l-octa-2,7-dienylacetamidomalonate 16 in 91% yield as a major product. Subsequent hydrogenation followed by hydrolysis gave octyl glycine 17 in 47% yield (Scheme 4). 

Dienes undergo dimerization-addition with various nucleophiles, such as alcohols, amines, enamines, and activated methylenes and methynes, in the presence of Pd(0) or Pd(ll) catalysts to afford the corresponding octa-2,7-dienyl derivatives. 

Direct Nucleophilic Substitution. Aminomercuration has been satisfactorily extended to additions to cyclo-octa-1,5-diene (Scheme 4). The high yield suggests that this reaction will be of considerable synthetic value. 

Structure determination of 2-benzenesulfonyl-3-trimethylsilylbicyclo[2.2.2]octa-2,5-diene (197) demonstrates that the electron-deficient double bond is pyramidalized in the exo direction. Nucleophilic attack by hydride (a conjugate reduction) on... 

The addition of various carbon and heteroatom nucleophiles to (bicyclo[5.1.0]-octadienyl)iron cations has been reported. Mostly, the nucleophile attacks at the terminus of the dienyl system to form substituted (bicyclo[5.1.0]octa-2,4-diene)iron complexes. The nucleophile stereoselectively attacks from the rear side of the dienyl system, opposite to the iron atom. The method can be used for the synthesis of cis-2-(2 -carboxycyclopropyl)glycine (CCG-III) (Scheme 4-180). ... 

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