Cyclohepta-1,3-diene complexes

Another tandem synthesis based on rhodium-carbene complexes, the cyclo-propanation-Cope rearrangement sequence 8-68, was extensively investigated by Davies and coworkers (review Davies, 1993). This sequence leads to cyclohepta-dienes (8.154), which are useful for the synthesis of important natural products containing densely functionalized seven-membered rings. The sequence 8-68 requires ready access to 3-diazoalk-l-enes (vinyldiazomethanes) as basis for the rhodium-... 

This reacts with cycloocta-1,5-diene or ewdo-dicyclopentadiene to give [Cu(diolefin)2]03S-CF3 complexes, and with cyclooctatetrene, cyclo-dodeca-l,5,9-triene, cycloocta-1,3-diene, or norbomylene to give Cu(olefin)03S-CF3 complexes cyclohepta-l,3,5-triene can replace benzene in the parent complex yielding Cu(CFgS03) J(triolefin). 

Ruthenium(II) complexes may also be used to oxidize N-Boc hydroxylamine in the presence of tert-butylhydroperoxide (TBHP) to the corresponding nitroso dieno-phile, which is subsequently trapped by cyclohexa-1,3-diene to give the hetero Diels-Alder adduct (Entry 1, Scheme 10.26) [51]. A triphenylphosphine oxide-stabilized ruthenium(IV) oxo-complex was found to be the catalytically active species. Use of a chiral bidentate bis-phosphine-derived ruthenium ligand (BINAP or PROPHOS) result in very low asymmetric induction (8 and 11%) (Entry 2, Scheme 10.26). The low level of asymmetric induction is explained by the reaction conditions (in-situ oxidation) that failed to produce discrete, stable diastereomerically pure mthenium complexes. It is shown that ruthenium(II) salen complexes also catalyze the oxidation of N-Boc-hydroxylamine in the presence of TBHP, to give the N-Boc-nitroso compound which can be efficiently trapped with a range of dienes from cyclohepta-1,3-diene (1 h, r.t., CH2CI2, 71%) to 9,10-dimethylanthracene (96 h, r.t., CH2CI2,... 

A cycloheptenone precursor to the (+)-Prelog-Djerassi lactonic acid has been synthesized stereoselectively from cyclohepta-1, 3-diene using a nucleophilic addition-reactivation-nucleophilic addition sequence on iron complexes to introduce the required... 

The catalytic reaction of complex 49 with dtbcH2 and dioxygen is less selective than that of 50. In addition to the formation of dtbq and 3,5-di-ter -butyl-l-oxa-cyclohepta-3,5-diene-2,7-dione, some muconic acid anhydride and 2-pyrone derivatives are also produced as a result of both intra- and extradiol insertion of one of the oxygen atoms from dioxygen. Such products are consistent with the mechanism in Scheme 10, with the proviso that both the rhodium and iridium systems share the same mechanism, at least in the initial stages of the reaction. 

Cycloheptatriene does not react with Fe(CO)s to give the expected dicarbonyl complex 7i -C7H8Fe(CO)2, but forms instead a mixture of tricarbonyl complexes derived from cycloheptatriene and cyclohepta-1,3-diene (20, 35). This work, together with protonation and related reactions of the free double bond of 7r-C7HsFe(CO)3, have been summarized by Pettit and Emerson (118). More recently, Pettit and co-workers (101) have shown that (7-methoxycycloheptatriene)Fe(CO)3 is protonated by fluoro-boric acid with loss of methanol to give the ir-tropylium-iron tricarbonyl cation. 

Relatively little work has been done on complexes of cyclohepta-1,3-diene, and almost none on complexes of the 1,4-isomer. The iron tricarbonyl complex l,3-C7HioFe(CO)3 is obtained from Fe(CO)s and the diene, and also from Fe(CO)5 and cycloheptatriene 19,35). More recently, a complex of zero-valent iron containing only cyclohepta-l,3-diene and cycloheptatriene, has been obtained by a reductive Grignard reaction on ferric chloride (57). 

Nothing is known about the chelating tendencies of cydoocta-l,3-diene and cycloocta-1,4-diene with platinum(II). Methanolic Na2PdCU reacts with the 1,3-diene at room temperature to give a methoxy-substituted ir-allyl complex, while on heating ir-cycloocta-2,4-dienylpalladium(II) chloride is formed 122). The latter is also obtained from the diene and PdCl2 in acetic acid 82). Both complexes are similar to their cyclohepta-1,3-diene analogs (Section II, D). 

The alkoxy ir -allylic derivatives underwent alkoxyl exchange very readily when treated with the appropriate alcohol containing a little mineral acid (10" M)(e.g. methoxy-ethoxy and vice versa). These reactions are believed to go via an intermediate carbonium ion stabilised by the delocalised electron system of the tt-allylic group. Methoxy tt-allylic complexes derived from 2,5-dimethylhexa-2,4-diene, cyclohepta-1,3-diene and cycloocta-1,3-diene on heating lost methanol irreversibly to give a8-unsaturated tr-allylic complexes e.g. cyclohepta-1,3-diene first gave a tt-methoxycycloheptenyl and then a TT -cycloheptadienyl complex. 

Interratingly, irradiation for 6 h of the 1 1 complex 61 compc d of 8 a and 58 which had been prepared by keeping a solution of 8a and an equimolar amount of 58 in benzene-hexane at room temperature for 12 h (colorless needles of mp 133 to 136 °C) gave the optically active photocyclization product (—)-bk yclo[4.2.0]oct-7-en-2-one (62) Qa]p —60.6 (c 0.18, CHCI3)] in quantitative yield The photocyclization reaction is in contrast to the photodimerization of 58 in 59. In the case of 61, the photodimerization of 58 is probably prevented by steric hindrance. It is almost certain that one optical conformer of 58 is included in 61, but a real proof of this fact requires an X-ray structural study in the future. However, the formation of the optically active 62 is valuable, because photoreaction of 58 in solution does not give any intramolecular photocyclization product It has been reported that irradiation of bicyclo[5.1.0]octa-3,5-dien-2-one (63) in methanol leads to a mixture of racemic tricyclo[4.2.0.0 ]oct-7-en-2-one (65), 37, and cyclohepta-l,3,5-triene Control of the reaction was also tried in expectation... 

Both cis- and Irons- divinylcyclopropane form complexes with hexafluoroacetonyl-acetonatorhodium(i). In the former, (276), the cyclopropane ring remains intact, while in the latter, (277), X-ray analysis has shown the ring to be essentially open. Complex (276) undergoes dissociation. Cope rearrangement, and recomplexation, while (277) is stable. Cyclohepta-1,4-diene emanates only from the cis-isomer in a mixture of... 

Cyclohepta-l,3-diene and ruthenium(iii) chloride trihydrate react in the presence of zinc dust and ethanol to give (329). Complex (329) was also obtained from [(C7Hio)RuCl2] and isopropyl magnesium bromide in the presence of cyclohepta-... 

Platinum(o) complexes of cyclohepta-, cyclo-octa-, and cyclonona-1,2-dienes have been observed complexing ability increases with decrease in ring size. ... 

Complexes of cycloheptatriene and cyclohepta-1,3-diene with various metals are reported. ... 

Cyclohepta-3,5-dienone)iron complexes can be stereoselectively methylated and hydroxylated. The electrophile adds exclusively anti to the tricarbonyliron fragment. Double methylation or hydroxylation of the a and a positions is accomplished in high overall yield (Scheme 4-146). Silyl enol ethers adjacent to tricarbonyl(Ti -diene)iron units can be subjected to Mukaiyama aldol reaction with aldehydes to provide aldol adducts with varying diastereoselectivity. This methodology has, for example, been applied to the enantioselective synthesis of the dienetriols streptenol C and D (Scheme 4-147). ... 

Trimerization of alkynes to form aromatic compounds has been achieved first by Reppe and Schweckendiek using nickelcarbonyl complexes as catalysts. The applicability of carbonyliron complexes for this purpose was reported as early as 1960. Unsymmetric acetylenes give exclusively the arenes with symmetric substitution pattern under these conditions (Scheme 4-309). Alternatively, (Ti -arene)iron complexes such as bis(ethene)(toluene)iron can be used for the cyclotrimerization of unsymmetric alkynes. A variety of symmetrically substituted benzene derivatives has been obtained. Another very active precatalyst for this reaction is (Ti -cyclohepta-l,3,5-triene)(T -cycloocta-l, 5-diene)iron(0). ... 

Some reactions of cyclohepta- and cyclohexa-dienyl iron tricarbonyl complexes resemble the reactions of the jr-cyclopentadienyl iron analogues. However, ring addition reactions which give diene derivatives occur more readily [263c], e.g. 

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