Iron carbonyl complexes ketone synthesis

The synthesis of metal-coordinated 1-azirines and the reactions of azirines induced by metals have opened a new area in the chemistry of this small ring heterocycle. Many of the reactions encountered bear resemblance to previously discussed thermally and photo-chemically induced reactions of 1-azirines. The reaction of a series of diiron enneacarbonyls in benzene results in coupling and insertion to give diimine complexes and ureadiiron complexes as well as pyrroles and ketones (76CC191). A mechanism for the formation of these products which involves initial 1,3-bond cleavage and generation of a nitrene-iron carbonyl complex as an intermediate was proposed. 

The complex functions as a convenient source of the tricarbonyliron moiety by displacement of the unsaturated ketone. For example, reaction with 1,3-cycloheptadiene results in a 78% yield of (//-l,3-cycloheptadiene)tricar-bonyliron. More importantly, it may be used in syntheses of tricarbonyl-(diene)iron complexes where the iron carbonyls are not satisfactory. Several complexes of sensitive heptafulvenes have been prepared in this way, and the reagent has been used in the synthesis of tricarbonyliron complexes of several steroids. 

It is not always necessary to start with gem-dihalides for the synthesis of aldehydes or ketones. There is a process by which carbonyl compounds can be obtained from monohalides, sometimes in excellent yield for instance, when 3-chlorocyclopentene is stirred vigorously with aqueous sodium dichromate solution at 0°, a chromium complex of 2-cyclopenten-l-one is formed, and this is decomposed to give a 60-68% yield of the ketone if 50% sulfuric acid is dropped in carefully with cooling 513 and 1,2-cyclopentanedione can be obtained in 80% yield by dropwise addition of aqueous iron(m) chloride solution to 2-chlorocyclopentanone in water with rapid stirring at 100°.539... 

A variety of carbonyl reactions can be performed with aldehyde groups adjacent to (diene)iron complexes. This includes cyanohydrin formation as part of a synthesis employing sequential stereoselective introduction of nucleophiles to (diene)iron complexes with concomitant elongation of the carbon chain (see also Scheme 4-155). 370,371,374,375] reactions of aldehydes adjacent to (diene)iron complexes with methyl ketones have been reported. Diastereoselective intramolecular Mannich reaction of a... 

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