There
is a strong parallel between simple alcohol oxidation and
carbonyl desaturation from both strategic and tactical vantage points.
As they both seek to extract hydrogen from an organic substrate, they
are deceptively simple looking transformations that have been addressed
over the past 70+ years through stoichiometric means. The past decade
has seen an intensifying level of interest in rendering both of these
simple reactions catalytic. In this Perspective, recent advances from
the past 5 years are highlighted featuring both transition-metal-catalyzed
and metal-free approaches to carbonyl desaturation. Through a historical
overview and a detailed look at each of these new developments, we
seek to address the question of in what context a catalytic strategy
emerges as ideal.
An
addition-carbocyclization cascade reaction initiated by arylboronic
acids and catalyzed by a rhodium/chiral diene complex is described.
Starting from N-bridged yne-enoate derivatives, chiral
functionalized seven-membered 3-benzazepine heterocycles were obtained
with high enantioselectivities, thanks to a rhodium 1,4-shift.
The formation of chiral 5- and 7-membered
tetrahydrofurans and
tetrahydrobenzo[d]oxepines is achieved via arylative
cyclization of simple O-tethered alkyne-enoates in
the presence of arylboronic acids and chiral dienes-rhodium catalyst
under mild conditions. Access to such structures was achieved via
a simple switch in the regioselectivity of the alkyne insertion thanks
to a proper choice of the alkyne substituent.
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