Tricarbonylcyclohexadienyliron complexes : synthetic equivalents of aryl cations; a facile synthesis of 2-aryl-cyclopentenones and its application towards prostaglandin analogues

Stereochemical Requirements of Oxidative Cyclizations in Extended Iterative Organoiron-Mediated Routes to Alkaloids

“…The majority of oxidative conditions used in this study formed either the aldehyde 11 or the required cyclization product 10 , but the ferrocenium ion procedure, which had proved very effective in the examples examined by Knölker, failed to produce an isolable product or, when used in the presence of sodium carbonate to control the build-up of acid, proved unreactive (Table ). The hypervalent iodine reagents behaved differently, with IBX showing selectivity for the aldehyde 11 and PIFA producing 10 .…”

“…In order to quickly test a range of oxidizing conditions, a model compound 9 (Scheme ) was chosen. The substrate 9 contains the (η 4 -cyclohexadiene)iron(0) complex and benzyl alcohol structures present in 1 (Figure ) and was easily made in the racemic series in two steps starting from “Birch’s salt” (±)- 7 using a diaryl cuprate reagent 6 generated from the aryllithium reagent used in our earlier studies of the preparation of 1-arylcyclohexadienyliron complexes. The aryllithium and copper iodide produced the diaryl cuprate species 6 which on addition of 2-methoxy salt 7 gave the exo adduct 8 , which was taken on to the benzyl alcohol in the presence of a small quantity of methyl 3,4-dimethoxybenzyl ether, which was produced when the excess diaryl cuprate was quenched with water.…”

Ring Expansion of Cyclobutylmethylcarbenium Ions to Cyclopentane or Cyclopentene Derivatives and Metal-Promoted Analogous Rearrangements

“…The mechanism involved coordination of AlCl 3 to the carbonyl oxygen, followed by ring expansion to form a sulfur-stabilized carbenium ion, and migration of the alkyl group to the carbenium ion center with concomitant regeneration of the carbonyl function to afford the corresponding cyclopentanones. This reaction was applied to the synthesis of 2-[4-(3-hydroxypropyl)phenyl]-2-cyclopentenone 289 in 84% yield from 287 , which is of interest because the corresponding carboxylic ester was proposed as a key intermediate for the synthesis of 4,5,6,7-tetra- nor -3-8-inter- p -phenylene-11-deoxyprostaglandin, a new prostaglandin analogue. , …”

New chemical and stereochemical applications of organoiron complexes

“…The addition of carbon nucleophiles to simple cyclohexadienyl-Fe(CO) 3 cations also provided an opportunity to examine the potential of these complexes as aryl cation equivalents [ 376 ] suitable for application to total synthesis. This was demonstrated by the synthesis of alkaloid (±)- O -methyljoubertiamine 184 [ 117 , 118 , 377 ] ( Scheme 34 ).…”

“…The foregoing procedure demonstrates that efficient synthesis of complex, para -substituted anisole derivatives is extremely simple using organoiron precursors [ 376 ], and that the resulting cyclohexadiene-Fe(CO) 3 complexes can be used in an alternative approach to natural-product syntheses [ 89 , 113 , 381 – 383 ], for example, for the synthesis of quassinoid-type natural terpenes having high antitumor activity [ 384 ]. The total synthesis of the natural diterpene aphidicolin (active against herpes virus) involves cyclocarbonylation with sodium iron tetracarbonyl [ 385 ].…”