1,4-Pentadiene with carbonyl complexes

With the low-valence iron pentacarbonyl, vinylcyclopropanes 22 are thermally transformed to the diene re-complexes, the (1,3-trans-pentadiene)iron carbonyl complexes 23, through bond fission, 1,2-hydrogen shift, and stereoselective coordination [15]. (Scheme 9)... 

Nonconjugated dienes are rearranged to iron carbonyl complexes of conjugated dienes when treated with FefCOjs or Fe3(CO)i2. Thus 1,4-pentadiene gives tmw -l,3-pentadieneiron tricarbonyl (34) possibly by the route ... 

Zirconocene complexes (with s-cis geometry) of isoprene, 2,3-dimethylbutadiene, and 3-methyI-I,3-pentadiene are reported to give exclusively 1 1 addition with carbonyl substrates even if these are used in excess and the reaction temperature is fairly high (ca. 100 C). On the contrary, zirconocene complexes of 5-ci5-butadiene, 1,3-pentadiene, and 2,4-hexadiene ca, 1 1 mixture of the s-cis and s-trans isomers) easily accept (equation 53) 2 equiv. of either butanal or 3-pentanone, at low temperature ca. 30 C) in high yields (95%). This can be exploited for the stepwise insertion of two different electrophiles... 

The indium-mediated reaction of cinnamyl bromide with 5-formyluracil derivatives gives the corresponding homoallylic alcohols. The presence of C-4 carbonyl is essential for high diastereoselectivity owing to complexation with indium (Scheme 8.32) [49]. Pentadienylindium, a vinylog of allylindium, reacts with carbonyl compounds selectively at the y position to give 1,4-pentadiene derivatives (Scheme 8.33) [50]. 

Complexes 17-19 can be written in one valence structure as a, /3-unsaturated carbonyl compounds in which the carbonyl oxygen atom is coordinated to a BF2(OR) Lewis acid. The C=C double bonds of such organic systems are activated toward certain reactions, like Diels-Alder additions, and complexes 17-19 show similar chemistry. Complexes 17 and 18 undergo Diels-Alder additions with isoprene, 2,3-dimethyl-1,3-butadiene, tram-2-methyl-l,3-pentadiene, and cyclopentadiene to give Diels-Alder products 20-23 as shown in Scheme 1 for complex 17 (32). Compounds 20-23 are prepared in crude product yields of 75-98% and are isolated as analytically pure solids in yields of 16-66%. The X-ray structure of the isoprene product 20 has been determined and the ORTEP diagram (shown in Fig. 3) reveals the regiochemistry of the Diels-Alder addition. The C-14=C-15 double bond distance is 1.327(4) A, and the... 

Reaction of 3,3-disubstituted-l,4-pentadiene 92 with a primary amine under cyclohydrocarbonylation conditions yielded cyclopenta[. ]pyrrole 96 as the predominant product accompanied by a small amount of cyclopentanone 95 (Scheme 15). This unique reaction is proposed to proceed through a cascade hydrocarbonylation-carbonylation process. The first hydrocarbonylation of 92 and the subsequent carbocyclization formed cyclopentanoylmethyl-Rh complex 93. If 93 immediately reacts with molecular hydrogen, 2-methylcyclopentanone 95 is formed. However, if CO insertion takes place faster than the hydrogenolysis, cyclopentanoylacetyl-Rh complex 94 is generated, which undergoes the Paal-Knorr condensation with a primary amine to yield cyclopenta[. ]pyrrole 96. ... 

There has been one report of an rj1 -pentadienyl complex of a transition element, Cp2Zr(2-MeC5H6)2, prepared from Cp2ZrCl2 and 2-methyl-pentadienylpotassium (155). Cp2ZrHCl, however, give -complexes of 1,3-pentadiene and its higher homologs, when treated with pentadienyl-potassiums. The reactions of these products with alkenes, alkynes, dienes, and carbonyl compounds are synthetically important (156). 

The formulas of 37-39 show the substitution of three carbonyls by a conjugated diene. Due to the fact that dienes are four-electron donors, the complexes are electron-deficient species. The electron deficiency is reduced by formation of C—H—Cr three-center, two-electron bonds, previously found for a number of other complexes (43). When 2-methyl-5-isopropyl-l,3-cyclohexadiene is used as a potential ligand, the expected complexes 37r and 39r are not obtained, but instead complexes with the isomeric l-methyl-4-isopropyl-l,3-cyclohexadiene group (37r and 39r ) are formed [Eq. (19)]. Similarly, lk and 11 form not only the corresponding complexes 39k and 391, but also the isomeric complexes with (Z)-l,3-hexadiene (39k ) and with (Z)-2-methyl-1,3-pentadiene (391 ). 

As with the pentadienes, the complex formed with cyclopentadiene is dependent upon the iron carbonyl employed. 

Transmetallation of 1-6 or treatment of 1-6 with Lewis acid further broadens the scope of its reaction chemistry. In the presence of CuCl, the reaction of 1-6 with diazo dicarboxylate affords pyridazine derivatives [27]. In the presence of CuCl or nickel complexes, the reaction of 1-6 with alkynes leads to benzene derivatives [28, 29]. Transmetallation of 1-6 with Bids allows further reaction with 2-oxo malonate to give 2/7-pyran derivatives [27]. Transmetallation of 1-6 with CrCls followed by reaction with isocyanates affords pyridine derivatives [30]. Transmetallation of 1-6 with AICI3 followed by reaction with aldehydes affords pentasubstimted cyclo-pentadiene derivatives [31]. Under the similar condition, 1-6 reacts with nitroso compounds to form pyrrole derivatives [32]. Addition of n-butyl lithium activates 1-6 and allows further reaction with carbon monoxide, which leads to carbonylation and affords 2-cyclopentenone upon hydrolysis [33]. 

Reactions of diene-Fe(CO)3 complexes with other molecules capable of forming ligands with metals in low oxidation states can result in either displacement of the diene ligand or of one of the carbonyl groups. For example, the Fe(CO)3 complexes of with triphenylphosphine with liberation of the hydrocarbon ligands 34,19). Cyclooctatetraene-iron tricarbonyl gives cyclooctatetraene when treated with P 3 but with As 3 or Sb 3 the... 

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