Synthesis of the spirastrellolide A, B/C spiroketal: enabling solutions for problematic Au(I)-catalyzed
Barry B Butler1, Jagadeesh Nagendra Manda1, Aaron Aponick1
1Department of Chemistry, Center for Heterocyclic Compounds, University of Florida, Gainesville, Florida 32611, United States.
Abstract:
A synthesis of the spirastrellolide A, B/C-ring monounsaturated spiroketal is reported. The key step relies on a Au-catalyzed spiroketalization of a propargyl triol employing an acetonide as a regioselectivity regulator. Through observation and analysis, a set of conditions has been developed that facilitates the use of a mixture of diastereomeric substrates, obviating the need to control the stereochemistry of the propargyl stereocenter and enabling a convenient retrosynthetic disconnection. The key reaction proceeds in 80% yield in 1 min at ambient temperature with the Me3PAuCl/AgOTf catalyst system. These conditions should be widely applicable for new synthetic endeavors as they appear to overcome all issues with the Au-catalyzed spiroketalization.
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