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1.7.3.1.1 From Dienes without Rearrangement

DOI: 10.1055/sos-SD-001-00654

Stephenson (Product Subclasses 17), G. R.; Perseghini, M.; Togni (Product Subclass 8), A.Science of Synthesis, (20011778.

A variety of sources of tricarbonyliron allow the attachment of the ironcarbonyl unit to 1,3-dienes 94 and 97 (Scheme 26). The use of nonacarbonyldiiron, Fe2(CO)9, is most straightforward, as gentle heat[‌325‌] or ultrasonic irradiation[‌326‌] splits the dinuclear carbonylmetal complex into pentacarbonyliron, Fe(CO)5, and tetracarbonyliron, Fe(CO)4. Once tetracarbonyliron is coordinated to the diene, rapid loss of a carbonyl ligand completes the formation of the tricarbonylironη4-diene complex. Heating of the trinuclear dodecacarbonyltriiron, Fe3(CO)12,[‌176‌,‌327‌] or photolysis of pentacarbonyliron,[‌176‌,‌328‌] similarly lead to tetracarbonyliron, which can be used in the complexation of dienes. Further mild procedures for obtaining tetracarbonyliron or tricarbonyliron are available. Tetracarbonyliron can be transferred from tetracarbonylironamine complexes[‌329‌] and from pentacarbonyliron by oxidative removal of a carbonyl ligand by use of trimethylamine N-oxide.[‌330‌] Transfer of tricarbonyliron is possible from (benzylideneacetone)tricarbonyliron (103)[‌331‌] (see Section 1.7.3.7) or its anisyl analogue 101, and from (azadiene)tricarbonyliron complexes.[‌332‌,‌333‌] The azadiene method has been developed so that the transfer reagent could be retained on a solid support, and so that both equivalents of iron in nonacarbonyldiiron could be utilized; this method can also be employed with pentacarbonyliron.[‌334‌,‌335‌] Catalytic quantities of azadienes (e.g., 100) have been used.[‌334‌] In the reaction of oxa- and azadienetricarbonyliron complexes with diene ligands, one alkene in the 1,3-diene displaces the ketone portion of the enone (or the C=N link in the azadiene) from iron as the first step. A similar stepwise alkene displacement transfers tricarbonyliron from Grevels' reagent, tricarbonylbis(η2-cis-cyclooctene)iron(0).[‌336‌] The benzylideneacetone method provides a solution to the problem of formation of the complex consisting of tricarbonyliron bound to the B ring of ergosteryl acetate,[‌337‌] and is suitable for the transfer of dicarbonyl(triphenylphosphine)iron, [Fe(CO)2PPh3], (from 102) and dicarbonyl(triphenyl phosphite)iron, [Fe(CO)2P(OPh)3], groups (e.g., to form phosphine complex 99).[‌338‌] Substituted benzylideneacetone complexes such as 101 are very effective.[‌335‌] Because reaction conditions are gentle, the position of the diene in the complex (e.g., 28, 48, 98) is usually the same as in the starting material, so the problem of regioselective synthesis of η4-complexes with specific substitution patterns by these methods reduces to the classic problem of regioselective preparation of the 1,3-dienes themselves [see Science of Synthesis, Vol. 46 (1,3-Dienes)]. Cationic η4-diene complexes can be made by photolysis of the diene with [FeCp*(CO)2]+•THF[‌170‌] (see Section 1.7.2.2.5).

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Meeeeee M8 M8 M Meeeeeeeee Meeee (%) Mee
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