Organocatalytic 1,4-conjugate addition of ascorbic acid to α,β-unsaturated aldehydes: bio-inspired total syntheses of leucodrin, leudrin and proposed structure of dilaspirolactone
The organocatalytic additions of ascorbic acid to various α,β-unsaturated aldehydes via tandem 1,4-conjugate addition/hemiacetalization/hemiketalization were developed, which provided a rapid entry into the 5-5-5 spirodilactone cores of a family of ascorbylated natural products. Based on the described chemistry, total syntheses of leucodrin, leudrin and the proposed structure of dilaspirolactone were achieved.
Asymmetric Total Synthesis of a Bioactive Lignanamide Using a 5‐
<i>endo</i>
‐
<i>tet</i>
‐Type Cyclization of Activated Cyclopropylcarbinols and Synthetic Support for the Reaction Mechanism
The first enantioselective total synthesis of a bioactive lignanamide with high enantiomeric excess was accomplished. The key synthetic steps include an organocatalytic enantioselective cyclopropanation and a Lewis-acid-mediated chirality-transferring 5-endo-tet-type cyclization of a D−A cyclopropylcabinol, which proceeds with a very high level of stereoinduction. Based on the obtained experimental