Asymmetric Synthesis of Cyclobutanones: Synthesis of Cyclobut-G

A simple, efficient, and stereoselective approach has been developed for obtaining chiral cis- and trans-disubstituted cyclobutanones from readily available alkyl- and functionalized alkyl-substituted enol ethers. The usefulness of these cyclobutanones is illustrated by an enantioselective synthesis of cyclobut-G (Lobucavir)

Intermolecular C–H Amination of Complex Molecules: Insights into the Factors Governing the Selectivity

Transition-metal-catalyzed C–H amination via nitrene insertion allows the direct transformation of a C–H into a C–N bond. Given the ubiquity of C–H bonds in organic compounds, such a process raises the problem of regio- and chemoselectivity, a challenging goal even more difficult to tackle as the complexity of the substrate increases. Whereas excellent regiocontrol can be achieved by the use of an appropriate tether securing intramolecular addition of the nitrene, the intermolecular C–H amination remains much less predictable. This study aims at addressing this issue by capitalizing on an efficient stereoselective nitrene transfer involving the combination of a chiral aminating agent <b>1</b> with a chiral rhodium catalyst <b>2</b>. Allylic C–H amination of terpenes and enol ethers occurs with excellent yields as well as with high regio-, chemo-, and diastereoselectivity as a result of the combination of steric and electronic factors. Conjugation of allylic C–H bonds with the π-bond would explain the chemoselectivity observed for cyclic substrates. Alkanes used in stoichiometric amounts are also efficiently functionalized with a net preference for tertiary equatorial C–H bonds. The selectivity, in this case, can be rationalized by steric and hyperconjugative effects. This study, therefore, provides useful information to better predict the site of C–H amination of complex molecules

Total Synthesis of (−)-Himalensine A

The first enantioselective synthesis of (−)-himalensine A has been achieved in 22 steps. The synthesis was enabled by a novel catalytic, enantioselective prototropic shift/furan Diels–Alder (IMDAF) cascade to construct the ACD tricyclic core. A reductive radical cyclization cascade was utilized to build the B ring, and end-game manipulations featuring a molecular oxygen mediated γ-CH oxidation, a Stetter cyclization to access the pendant cyclopentenone, and a highly chemoselective lactam reduction delivered the natural product target

Total Synthesis of (−)-Himalensine A

The first enantioselective synthesis of (−)-himalensine A has been achieved in 22 steps. The synthesis was enabled by a novel catalytic, enantioselective prototropic shift/furan Diels–Alder (IMDAF) cascade to construct the ACD tricyclic core. A reductive radical cyclization cascade was utilized to build the B ring, and end-game manipulations featuring a molecular oxygen mediated γ-CH oxidation, a Stetter cyclization to access the pendant cyclopentenone, and a highly chemoselective lactam reduction delivered the natural product target

Total Synthesis of (−)-Himalensine A

The first enantioselective synthesis of (−)-himalensine A has been achieved in 22 steps. The synthesis was enabled by a novel catalytic, enantioselective prototropic shift/furan Diels–Alder (IMDAF) cascade to construct the ACD tricyclic core. A reductive radical cyclization cascade was utilized to build the B ring, and end-game manipulations featuring a molecular oxygen mediated γ-CH oxidation, a Stetter cyclization to access the pendant cyclopentenone, and a highly chemoselective lactam reduction delivered the natural product target