Overcoming the inherent difficulty to prepare quaternary carbon stereogenic centers, the diastereo‐ and enantioselective preparation of acyclic carbon backbones possessing vicinal quaternary and tertiary stereogenic centers (i.e. in a 1,2‐relationship) causes distorted geometries and represents a very acute problem in organic synthesis. Several approaches are discussed in this minireview underlining the challenges illustrated by the rather limited number of approaches available to practitioners.
Synthetic organic strategies that enable the catalytic and rapid assembly of a large array of organic compounds that possess multiple stereocentres in acyclic systems are somewhat rare, especially when it comes to reaching today's high standards of efficiency and selectivity. In particular, the catalytic preparation of a three-dimensional molecular layout of a simple acyclic hydrocarbon skeleton that possesses several stereocentres from simple and readily available reagents still represents a vastly uncharted domain. Here we report a rapid, modular, stereodivergent and diversity-oriented unified strategy to construct acyclic molecular frameworks that bear up to four contiguous and congested stereogenic elements, with remarkably high levels of stereocontrol and in only three catalytic steps from commercially available alkynes. A regio- and diastereoselective catalytic Heck migratory insertion reaction of alkenylcyclopropyl carbinols that merges selective C-C bond cleavage of a cyclopropane represents the key step.
We report the first enantioselective organocatalyzed domino synthesis of azepane moieties. This temporary-bridge strategy is based on a conceptually original annulation of ambident electrophilic and 1,4-bis-nucleophilic α-ketoamides with 1,3-bis-electrophilic enals. The obtained oxygen-bridged azepanes can be selectively transformed into optically active azepanone, azepanol or azepanedione derivatives of high synthetic value.
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