Iron tricarbonyl complexes alkylation

Stereoselective Michael addition of lunctionalized zinc-copper reagents to cycloheptatrienone iron tricarbonyl complexes is observed (Scheme 146). A pendant nitrile can participate in an alkylation reaction of the intermediate enolate forming a fused bicyclic ring system (Scheme 147). Addition in a 1,2- or 1,4-fashion depends on the nucleophile. Harder nucleophiles tend to form 1,2-adducts (Scheme 148). 

Cyclobutadiene iron tricarbonyl complexes also stabilized carbocations on an adjacent carbon. The cation reacts with silyl enol ethers to afford alkylated complexes such as (127) (Scheme 187). A samarimn diiodide -mediated intermolecular radical cychzation of iron tricarbonyl complex (128) is depicted in Scheme 188. An excellent stereocontrol at three contiguous centers is observed. 

Dienes form very stable complexes with a variety of metal caibonyls, particularly Fe(CO)s, and the neutral V-diene metal carbonyl complexes are quite resistant to normal reactions of dienes (e.g. hydrogenation, Diels-Alder). However, they are subject to nucleophilic attack by a variety of nonstabilized carbanions. Treatment of -cyclohexadiene iron tricarbonyl with nonstabilized carbanions, followed by protonolysis of the resulting complex, produced isomeric mixtures of alkylated cyclohexenes (Scheme 15).24 With acyclic dienes, this alkylation was shown to be reversible, with kinetic alkylation occurring at an internal position of the complexed dienes but rearranging to the terminal position under thermodynamic conditions (Scheme 16).2S By trapping the kinetic product with an electrophile, overall carbo-... 

Lithium alkynylcuprates react with haloallenes to give similar skipped diacetylenes (see below). The related skipped enynes can be prepared by treatment of (pentadienyl)iron(tricarbonyl) halide complexes with dilithium trialkynylcuprates, the compounds being isolated as the iron(tricarbonyl)(diene) complexes (Scheme 4). Further examples of alkylation reactions of copper alkynides are illustrated in Scheme 5. Reaction between a lithium cyanoaikynecuprate and an iodoallene leads to a skipped diacetylene. This useful reaction has been used by Corey in his synthesis of hybridalactone (Scheme 6). °... 

Bicyclo[4.1.1] or [3.2.1]octenones and cyclopropanes have resulted from decomplexation of the iron tricarbonyl group from the alkyl-allyliron tricarbonyl complex, using oxidative (i.e., GO atmosphere) or carbonylative methods for the bicyclooctenones and ceric ammonium nitrate (GAN) for the cyclopropanes. Photolysis of analogous tricarbonyl iron complexes leads to monoolefmic hydrocarbons or aldehydes. The kinetics of GO substitution in reactions of 77 -cyclopropenyl complexes of iron is also reported. " A number of comprehensive reviews have appeared since 1992, illustrating the chemistry of ry -allyliron complexes. 

There exists a limitation to this direct method of synthesis in the case of acyclic dienes having m-alkyl substituents. Although these compounds may give rise to diene-Fe(CO)3 complexes, the ligand in the complex invariably involves a rearranged diene and, as of now, no m-substituted acyclic diene appears to have been prepared by the direct reaction. For example, 2,5-di-methyl-2,4-hexadiene (XVII) reacts with Fe(CO)5 to give trans-2,S-6x-methyl-l,3-hexadiene-iron tricarbonyl (XVIII) 41). Likewise, 4-methyl-1,3-pentadiene (XIX) gives ra r-2-methy 1-1,3-pentadiene-iron tricarbonyl... 

ALKYLATION OF DIMEDONE WITH A TRICARBONYL(DIENE)IRON COMPLEX TRlCARBONYL[2-[(2,3,4,5-t))-4-METHOXY 2,4 CYCLOHEXADUEN-l-YLJ-5,5-DIMETHYL-l,3-CYCLOHEXANEDIONE]IRON... 

With the successful chemistry of the cymantrenes and the (cyclobuta-diene)tricarbonyl iron, the quest for tetraethynylated cyclobutadienes based on CpCo-stabilized complexes arose. Why would they be interesting Whereas all derivatives of 63 and 68 exhibit reasonable stability when their alkynyl substituents are protected by either an alkyl or a trimethylsilyl group, the desilylated parents are isolated only with difficulty and are much more sensitive. 

Cyclopropanation reactions of nonheteroatom-stabilized carbenes have also been developed. The most versatile are the cationic iron carbenes that cyclopropanate alkenes with high stereospecificity under very mild reaction conditions. The cyclopropanation reagents are available from a number of iron complexes, for example, (9-alkylation of cyclopentadienyl dicarbonyliron alkyl or acyl complexes using Meerwein salts affords cationic Fischer carbenes. Cationic iron carbene intermediates can also be prepared by reaction of CpFe(CO)2 with aldehydes followed by treatment with TMS-chloride. Chiral intermolecular cyclopropanation using a chiral iron carbene having a complexed chromium tricarbonyl unit is observed (Scheme 61). 

Teatment of cyclooctatetraenetricarbonyliron complexes 10 with anhydrous aluminum trichloride in benzene gives tricarbonyl(2,4- j-8-or-9-oxabicyclo[3.2.2]nona-2,6-dien-8-yl)iron (11), which was previously obtained from tricyclo[3.3.1.0 ]nona-3,6-dien-9-one (12 barbaralone) with nonacarbonyldiiron. Conversion of this product 11 with carbon monoxide (100 atm, 120°C) yields barbaralone (12) in 95% yield. Thus, a high yielding (95%), short synthesis of barbaralone (12, R = H) from cyclooctatetraene via an alkyl-allyl complex intermediate 11 is available. 

Insertion of [Fe(CO)5] into the four-membered ring of a-pinene gave a a, allyl complex which was used for further synthesis. Alkylation of tricarbonyl iron diene and cationic dienyl complexes also gave o.ti allyl species. A o, allyl lactone complex was used to form the lactone ring in the synthesis of valilalactone, a p-lactone esterase inhibitor,and a related allyl lactam complex has been derived from prolineJ ... 

Tricarbonyl iron complexes of a number of substituted dihydroanisic esters have been prepared. Several undergo hydride abstraction to yield [(cyclo-hexadienyl)Fe(CO)3]+ salts, which react with malonate in the expected manner to give the 5-substituted (l,3-chd)Fe(CO)3 derivative. Hydrolysis of the parent salt (63) yields (cyclohexa-2,4-dienone)Fe(CO)3 containing the keto-isomer of phenol, and (63) may also be alkylated with dimedone to yield the 5-substituted (l,3-chd)Fe(CO)s complex. The bicyclic analogue (64) and... 

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