Iron carbonyl dienes

Diene Iron Carbonyl Dienes are most commonly protected with the Fe(CO)3 group. Once again, an oxidative deprotection step with FeCls is often used. One important application is the protection of a diene in the B ring of certain steroids (e.g., 14.9). Under these circumstances, the side chain... 

The double bond migration in steroid hydrocarbons catalyzed by acids or noble metals (see, for example, ref. 185) will not be discussed here. A general review of nonsteroid olefin isomerization has recently been published. Iron carbonyl has been used to isomerize steroidal dienes. 

Catenated Organic Compounds of the Group IV Elements, 4,1 Conjugate Addition of Grignard Reagents to Aromatic Systems, 1, 221 Cyclobutadiene Metal Complexes, 4, 95 Cyclopentadienyl Metal Compounds, 2, 365 Diene-Iron Carbonyl Complexes, 1, 1... 

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)... 

The iron carbonyl complex [Fe(CO)5] in basic media hydrogenated steroidal dienes selectively (equations 10-12)30. 

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 ... 

A diene system with unsymmetrical 1,4-disubstitution is converted to the iron carbonyl complex 1 which is resolved into its enantiomers. The aldehyde function is conformationally locked in the transoid position and is diastereofacially shielded from the bottom face. Nucleophiles attack from the top face with high selectivity. Alternatively, chain elongation leads to the triene 2 which is reacted with diazomethane. Cerium(IV) oxidation removes the metal and furnishes the substituted cyclopropane 3. 

Both conjugated and nonconjugated olefins form complexes with the transition-metal carbonyls. Despite the fact that the first known complex, Zeises salt K(PtC2H4Cl3), discovered in 1827, was that of a simple olefin, complexes of monoolefins are rather limited in number. However, nonconjugated diolefins (L) react with group-VI carbonyls to form complexes of the type LM(CO)4 an example is provided by tetracarbonyl-bicyclo-(2,2, l)hepta-2,5-diene chromium (2) (Fig. 1). In contrast, the iron carbonyls... 

A review of diene-iron carbonyl complexes has recently appeared (5) metal complexes of di- and oligoolefinic ligands have also been reviewed (6). A general review of olefin, acetylenic, and 7r-allylic complexes of transition metals is due to Guy and Shaw (7). 

The analogous cycloheptadienyl complex (5 equation 1) was similarly prepared by Dauben and Ber-telli,4 but the acyclic pentadienyl systems were a little more difficult to obtain. The triphenylmethyl cation does not remove hydride from tricarbonyl(frans-pentadiene)iron (6 equation 2). The corresponding c/s-pentadiene complex (7 equation 3) cannot be prepared directly from the diene and an iron carbonyl,... 

Iron carbonyls have been used in stoichiometric and catalytic amounts for a variety of transformations in organic synthesis. For example, the isomerization of 1,4-dienes to 1,3-dienes by formation of tricarbonyl(ri4-l,3-diene)iron complexes and subsequent oxidative demetallation has been applied to the synthesis of 12-prostaglandin PGC2 [10], The photochemically induced double bond isomerization of allyl alcohols to aldehydes [11] and allylamines to enamines [12,13] can be carried out with catalytic amounts of iron carbonyls (see Section 1.4.3). 

Iron carbonyls also mediate the cycloaddition reaction of allyl equivalents and dienes. In the presence of nonacarbonyldiiron a,a -dihaloketones and 1,3-dienes provide cycloheptenes (Scheme 1.5) [14,15]. Two initial dehalogenation steps afford a reactive oxoallyliron complex which undergoes a thermally allowed concerted [4 + 31-cycloaddition with 1,3-dienes. The 1,3-diene system can be incorporated in cyclic or heterocyclic systems (furans, cyclopentadienes and, less frequently, pyrroles). Noyori and coworkers applied this strategy to natural product synthesis, e.g. a-thujaplicin and P-thujaplicin [14, 16]. 

Diene-Iron Carbonyl Complexes and Related Species R. Pettit and G. F. Emerson Reactions of Organotin Hydrides with Organic Compounds Henry C. Kuivila Organic Substituted Cyclosilanes... 

Protection and Activation of 1,3-Dienes by the Coordination of Iron Carbonyls... 

The iron carbonyl-promoted [3 + 4] cycloaddition of bromo-ketones to. 1,3-dienes provides a convenient way, via 2-oxyallyIs, of synthesizing tropones and hence thujaplicins. The synthesis of nezukone (154 X = H)253 has been reported from a,a,a, a -tetrabromoacetone and 3-isopropylfuran. Similarly, from 2-isopropylfuran, /3-thujaplicin (154 X = OH) has been synthesized from the corresponding tropone by known methods, and a-thujaplicin synthesis requires isopropyl substitution in the ketone moiety.254 Karahanaenone (155) is a minor product from pyrolysis of the benzoate (156).149... 

Complexation reactions which give alkene complexes with greater than one iron carbonyl unit, or with more than one alkene unit per ion center, have been reported. Use of excess diene relative to the iron carbonyl source allows formation of (diene)[Fe(CO)4]2 complexes. Low-temperature... 

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