jo500748e_si_002.cif (19.32 kB)
Gold(I)-Promoted Heterocyclization of Internal Alkynes: A Comparative Study of Direct Metallate 5‑endo-dig Cyclization versus a Stepwise Cyclization
dataset
posted on 2014-06-20, 00:00 authored by Jonathan
M. French, Steven T. DiverWith cationic gold catalysts, internal
alkynes bearing both propargylic
acyloxy groups and tosylamide pronucleophiles were found to cyclize
to give either five- or six-membered ring nitrogen heterocycles. A
wide variety of gold catalysts, counterions, and solvents were examined
to elucidate their effect on product distribution. In most cases,
the direct 5-endo-dig cyclization was found to be
the major pathway leading to good yields of dehydropyrrolidine products.
Alkyne substrates bearing additional normal alkyl substituents at
the propargylic position gave dehydropiperidines as the major product.
This pathway is thought to proceed by way of a 1,2- Rautenstrauch
rearrangement to produce a vinyl gold(I) carbene, which undergoes
conjugate addition by the nitrogen pronucleophile. Structural and
electronic factors were studied in the nitrogen pronucleophile and
in the migrating acyloxy group. Each was found to have a minor effect
on the product ratio.