Novel domino processes for asymmetric construction of nitrogen and oxygen heterocycles.

摘要

The Stevens rearrangement of ammonium ylides has emerged as a powerful tool for accessing nitrogen heterocycles. In this project, several chiral ligands/Cu or Rh complexes and reaction conditions have been surveyed for the catalytic asymmetric ammonium ylide/Stevens [1,2]-shift process. However, these initial efforts did not reveal any suitable conditions.; Marine ladder toxins have attracted much attention in organic synthesis due to their unique nanoscale structures, scarcity, and extremely high biological potency. A cascade method for construction of trans-fused cyclic ethers has been developed. Under mild acidic conditions, alpha-hydroxy ketone substrates undergo several deprotections, subsequent ketalization to form oxygen-containing rings, and trapping of unstable intermediates to terminate the cascade process. alpha-Hydroxy ketone substrates were prepared via 1,4-hydrosilylation of suitable enones, using Wilkinson or Karstedt's catalysts and trialkylsilane, followed by catalytic dihydroxylation. After the symmetric 6,6-bis(pyran) compound was synthesized, a second 6,6-bis(pyran) with a geminal dimethyl group was synthesized to determine the relative stereochemistry of bis(pyran) compounds. Furthermore, two new and unexpected rearrangement products were isolated and fully characterized.