Achiral Counterion Control of Enantioselectivity in a Brønsted Acid-Catalyzed Iodolactonization
作者:Mark C. Dobish、Jeffrey N. Johnston
DOI:10.1021/ja301858r
日期:2012.4.11
Highly enantioselective halolactonizations have been developed that employ a chiral proton catalyst-N-iodosuccinimide (NIS) reagent system in which the Brønsted acid is used at catalyst loadings as low as 1 mol %. An approach that modulates the achiral counterion (equimolar to the neutral chiral ligand-proton complex present at low catalyst loadings) to optimize the enantioselection is documented for
The apple never falls far from the tree: S‐alkylthiocarbamate 1 (see scheme, NBP=N‐bromophthalimide) was prepared in high yield through a synthetic sequence involving a Newman–Kwart rearrangement of the corresponding O‐alkylthiocarbamates. Compound 1 was used to catalyze bromolactonization, thus providing enantioenriched δ‐lactones in excellent yield and enantioselectivity.
Catalytic Asymmetric Iodocyclization of<i>N-</i>Tosyl Alkenamides using Aminoiminophenoxy Copper Carboxylate: A Concise Synthesis of Chiral 8-Oxa-6-Azabicyclo[3.2.1]octanes
A newly developed aminoiminophenoxycoppercarboxylate (L7‐Cu‐OAc)‐catalyzed asymmetriciodocyclization of N‐Tosyl alkenamides gave O‐cyclized products in good yields with high enantioselectivity. From the O‐cyclized products, a skeletal transformation was succeeded in the synthesis of biologically important chiral 8‐oxa‐6‐azabicyclo[3.2.1]octanes. DFT calculations suggested that the acetoxy anion
A 3,3'-bis(aminoimino)BINOL ligand was newly designed and synthesized for the formation of a trinuclear Zn complex upon reaction with Zn(OAc)2. Using the harmony of the tri-zinc atoms, 1 mol% Zn3(OAc)4-3,3'-bis(aminoimino)binaphthoxide catalyzed asymmetriciodolactonization in up to 99.9% ee.
unimolecular Zn3(OAc)4–3,3′‐bis(aminoimino)binaphthoxide complex, a poly‐Zn3(OAc)4–3,3′‐bis(aminoimino)binaphthoxide (poly‐Zn) complex was prepared from 3,3′‐diformylbinaphthol, tetramine, and Zn(OAc)2. The first‐generation poly‐Zn catalyst (poly‐Zn1) was prepared from poly(aminoiminobinaphthol) and Zn(OAc)2. Although poly‐Zn1 showed high catalytic activity for iodolactonization, the catalyst could not be