A direct iron(III)-catalyzed Prins–Peterson
reaction involving
α-substituted γ-triphenylsilyl bis-homoallylic alcohols
and aldehydes is described. Thus, cis-Δ4-2,7-disubstituted oxepenes were synthesized in a diastereoselective
reaction using sustainable catalytic conditions (3–5 mol %).
This highly productive process is the result of a cascade of three
chemical events with the concomitant formation of a C–O bond,
a C–C bond, and a Δ4 endocyclic double bond,
through a Prins cyclization followed by a Peterson-type elimination.
This tandem reaction is chemoselective vs the classical Prins cyclization.
This minireview focuses on recent advances in the synthesis of seven-membered ring oxacycles, whether saturated, unsaturated, fused or isolated. We cover a remarkable variety of strategies and methods developed during the past two decades, based mainly on cyclizations, ring-closing metathesis, conjugate additions, and ring expansions. The cyclizations can be generated directly or triggered through an oxocarbenium ion, carbocation or iminium-type species. Also discussed [a] Prof.
A new method that
allows the complete control of the regioselectivity
of the hydrobromination reaction of alkenes is described. Herein,
we report a radical procedure with TMSBr and oxygen as common reagents,
where the formation of the
anti
-Markovnikov product
occurs in the presence of parts per million amounts of the Cu(I) species
and the formation of the Markovnikov product occurs in the presence
of 30 mol % iron(II) bromide. Density functional theory calculations
combined with Fukui’s radical susceptibilities support the
obtained results.
A highly efficient, diastereoselective, iron(III)-catalyzed intramolecular hydroamination/cyclization reaction involving α-substituted amino alkenes is described. Thus, enantiopure trans-2,5-disubstituted pyrrolidines and trans-5-substituted proline derivatives were synthesized by means of a combination of enantiopure starting materials, easily available from l-α-amino acids, with sustainable metal catalysts such as iron(III) salts. The scope of this methodology is highlighted in an enantiodivergent approach to the synthesis of both (+)- and (-)-pyrrolidine 197B alkaloids from l-glutamic acid. In addition, a computational study was carried out to gain insight into the complete diastereoselectivity of the transformation.
A new, direct, and diastereoselective synthesis of activated 2,3,4,6-tetrasubstituted tetrahydro-2H-pyrans is described. In this reaction, iron(III) catalyzed an S2'-Prins cyclization tandem process leading to the creation of three new stereocenters in one single step. These activated tetrahydro-2H-pyran units are easily derivatizable through CuAAC conjugations in order to generate multifunctionalized complex molecules. DFT calculations support the in situ S2' reaction as a preliminary step in the Prins cyclization.
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