An efficient synthesis of stereodefined tetrasubstituted acyclic all-carbon olefins has been developed via a bis(2,6-xylyl)phosphate formation of stereoenriched tertiary alcohols, followed by in situ syn-elimination of the corresponding phosphates under mild conditions. This chemistry tolerates a wide variety of electronically and sterically diverse substrates and generates the desired tetrasubstituted olefins in high yields and stereoselectivities (>95:5) in most cases. This stereocontrolled olefin synthesis has been applied to the synthesis of anticancer drug tamoxifen in three steps from commercially available 1,2-diphenylbutan-1-one in 97:3 stereoselectivity and 78% overall yield.
Results of density functional theory calculations on rearrangements of potential biosynthetic precursors to the sesquiterpenoid illisimonin A reveal that only some possible precursors, those with certain specific oxidation patterns, are rearrangement-competent.
Results of kinetic experiments and quantum chemical computations on a series of platinum-promoted polycyclization reactions are described. Analysis of these results reveal a reactivity model that reaches beyond the energetics of the cascade itself, incorporating an ensemble of pre-cyclization conformations of the platinum-alkene reactant complex, only a subset of which are productive for bi- (or larger) cyclization and lead to products. Similarities and differences between this scenario, including reaction coordinates for polycyclization, for platinum- and enzyme-promoted polycyclization are highlighted.
The results of quantum chemical calculations on putative biosynthetic carbocation cyclization/rearrangements leading to pupukeanane and related sesquiterpenes indicate that a secondary carbocation proposed as an intermediate is not a minimum on the potential energy surface and instead resides in a region of the potential energy surface associated with a plateau containing multiple exit channels.
Organocatalytic enantioselective 1,3‐dipolar [6+4] cycloadditions of pyrylium ion intermediates with fulvenes promoted by a chiral primary amine catalyst have been developed to proceed in moderate to good yields and high enantioselectivities. The resultant chiral bicyclo[6.3.0]undecane scaffold containing a transannular bridging ether is densely functionalised providing a rigid scaffold for further manipulations. Computational studies give important insights into the role of the primary amine catalyst. Analysis of the reaction shows that the catalytic reaction proceeds in a step‐wise manner and rationalises the stereochemical outcome of the reaction. Several stereoselective complexity‐generating transformations, facilitated by the diverse functional groups and transannular bridge, are presented, highlighting the versatility of the core towards a number of the cyclooctanoid natural products.
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