Total Synthesis and Determination of Absolute Configuration of Cryptorigidifoliol G.

The first asymmetric total synthesis of (1S,5R,7S)-cryptorigidifoliol G and (1S,5R,7R)-cryptorigidifoliol G of the proposed natural product was achieved. The key steps in the synthesis involved Keck-Maruoka allylation, our own developed protocol for the construction of the trans-2,6-disubstituted dihydropyran, iodolactonization, cross-metathesis, Prins cyclization, and cis-Wittig olefination reaction. A comparison of the NMR as well as analytical data and thorough analysis of the 2D NMR suggested that the absolute stereochemistry of the proposed natural product is (1S,5R,7S)-cryptorigidifoliol G.

[3,3]-Acyloxy Rearrangement-Triggered Regioselective Hydration of δ-Acetoxy-α,ß-Alkynoates/Halo Alkynes.

Herein, we report a simple, efficient, highly regioselective, and broad-scope hydration method that is facilitated by an unusual interception of an electrophilic intermediate by water generated via acetate group participation during [3,3]-acyloxy rearrangement. Various carboxylate-directing groups including acetate, acrylates, pivalates, benzoate or its derivatives, and those derived from bioactive natural products were successfully implemented to direct the regioselective hydration for various functionalized δ-acyloxy-ß-ketoester synthesis. The reaction pathway was further confirmed by 18O labeling experiments, and to the best of our knowledge, this is the first report of hydration through an electrophilic intermediate generated during [3,3]-acyloxy rearrangement. Synthetic application includes the synthesis of a modifiable C5-carbon chain, five-, six-, and seven-membered heterocycles, and natural product diversification.

Synthesis of γ-Acetoxy ß-Keto Esters Through Regioselective Hydration of γ-Acetoxy-α,ß-alkynoates.

The Au(I)-catalyzed regioselective hydration of γ-acetoxy-α,ß-acetylinic ester by the assistance of a neighboring carbonyl group has been developed. Varieties of simple primary, secondary, and tertiary γ-acetoxy-α,ß-acetylinic esters, even those bearing sensitive functional group in the remote reaction sites, are selectively hydrated to the corresponding ß-keto esters. The reaction tolerates a wide variety of other carboxylates, such as benzoates, propionates, acrylates, and pivalates, including chiral carboxylates with retention of the configuration. The broad substrate scope, including the derivatization of complex natural products and neutral and open air conditions, makes this atom economical approach very practical. (18)O labeling experiments disclose that the oxygen transposition occurs from the carboxylate group to the triple bond, not from water.