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 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.
The shortest enantioselective total syntheses of (+)-isolaurepinnacin
and (+)-neoisoprelaurefucin have been accomplished. These syntheses
were based on a common parallel synthetic strategy using Prins–Peterson
cyclization in their core construction. In only one step, a seven-membered
ring oxacycle with the correct
cis
-stereochemistry
ring closure and the Δ
4
position of the endocyclic
double bond in (+)-isolaurepinnacin was obtained. This unsaturation
was also necessary to accede to the bromodioxabicycle on (+)-neoisoprelaurefucin.
A new methodology for the synthesis of seven-membered
unsaturated
azacycles (tetrahydroazepines) was developed. It is based on the powerful
aza-Prins cyclization in combination with the Peterson-type elimination
reaction. In a single reaction step, a C–N, C–C bond
and an endocyclic double bond are formed. Under mild reaction conditions
and using iron(III) salts as sustainable catalysts, tetrahydroazepines
with different degrees of substitution are obtained directly and efficiently.
DFT calculations supported the proposed mechanism.
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