A New Synthesis of Optically Active Tetrahydropyrans and Tetrahydrofurans

Tricarbonyliron complexes: an approach to acyclic stereocontrol

“…Complex 54 results from exo attack of the primary alcohol on the generated pentadienyl cation 56 (Scheme 16). 28 Presumably isomerisation to the more stable cisoid geometry 57 is sufficiently rapid under the reaction conditions to compete with trapping of the cation hence the formation of the two (readily separable) products. Note that under the strongly acidic reaction conditions, the possibility that product formation is a reversible process and the reaction is under thermodynamic control cannot be discounted.…”

“…No products arising from isomerisation to a cisoid geometry were observed in this case which may be due to the kinetic favourability of five-membered ring formation resulting in a much more rapid trapping of the cation such that isomerisation is no longer a competing process (Scheme 17). 28 This may also suggest that product formation is not reversible (but see below).…”

Additions to Fe(CO)3−Dienal Complexes: Dependence of Diastereoselectivity on Lewis Acid

“…In contrast, the diastereoselectivity when nucleophiles are added to aldehyde-substituted Fe(CO) 3 −diene complexes (X = O, Y = H) is generally modest. The addition of Grignard reagents and alkyllithiums to such aldehydes generally occurs preferentially to the s-cis conformation, leading to 2 (X = OH, Y = H, Z = Nuc) rather than 3 with, at best, 80:20 selectivity. ,− Alkynyllithium reagents add in a similar fashion with a slightly higher level of diastereoselectivity . In contrast, Ti(IV)- and Al(III)-based reagents have been reported to modestly favor the production of 3 over 2 (X = OH, Y = H, Z = Nuc; 75:25 selectivity) .…”

The η4-Dienyl Tricarbonyliron Moiety in Heterocyclic Synthesis. A Rare 1,2-Migration of the Complexation Site as a Key Step for a Novel Stereoselective Preparation of trans-2,3-Disubstituted 1,4-Dioxanes

“…Having been strongly involved in the field of (η 4 -dienyl)tricarbonyliron complexes for the last decade, we were aware of the well-known protecting and/or stereodirecting properties attached to the complexing Fe(CO) 3 unit just as well as the strong stabilization of carbocations located at the α position of the coordination site. − For example, by relying on the known electrophilicity of such (η 5 -dienyl)tricarbonyliron(1+) cations and on the nature of a tethered pendant nucleophile Nu , their intramolecular trapping provides a useful route to various iron complexed chiral non racemic heterocycles, − as depicted in Scheme .

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