Kirmse–Doyle‐ and Stevens‐Type Rearrangements of Glutarate‐Derived Oxonium Ylides

Abstract

A novel chemoenzymatic synthetic cascade enables the preparation of densely decorated tetrahydrofuran building blocks. Here, the lipase-catalyzed desymmetrization of 3-alkoxyglutarates renders highly enantioenriched carboxylic acid intermediates, whose subsequent activation and oxonium ylide rearrangement by means of rhodium or copper complexes furnishes functionalized O-heterocycles with excellent diastereoselectivity. The two-step protocol offers a streamlined and flexible synthesis of tetrahydrofuranones bearing different benzylic, allylic or allenylic side chains with full control over multiple stereogenic centers.

α-Arylamino Diazoketones: Diazomethane-Loading Controlled Synthesis, Spectroscopic Investigations, and Structural X-ray Analysis

“…In fact, the addition of amines could trigger ketene formation events on acid halides featuring acidic α-protons, while realizing chemistry with big excesses of CH 2 N 2 (2–6 equiv, i.e., 200–600 mol %) poses serious questions on the real practicability of using such an hazardous reagent . The reliability of the method was further documented in the synthesis of enantiopure diazoketones, as reported in recent works by Deska and Gaich . Additionally, we also extended its use to the chemoselective acylation of different nucleophiles such as amines and alcohols in the biomass-derived solvent 2-methyltetrahydrofuran (2-MeTHF) …”

Ester Formation via Symbiotic Activation Utilizing Trichloroacetimidate Electrophiles

“…This is supported by the lack of Friedel-Crafts alkylation products in the results described in Table 3, even though benzyl trichloroacetimidate is known to alkylate aromatic systems like toluene when treated with strong Lewis acids which presumably proceeds through a carbocation. 29 Additionally, prenyl trichloroacetimidate 15 has been reported to provide a nearly 1:1 mixture of prenyl and tert-prenyl ethers in the presence of a strong Lewis acid (TMSOTf), 30 while in the esterification reaction with 15 ( Table 1) the prenyl ester is highly favored and only a small amount of the tert-prenyl ester is observed. These results imply that some imidate esterifications with less reactive imidates may not be proceeding through a discreet carbocation.…”

Recent Advances in Asymmetric [1,2]-Stevens-Type Rearrangement via Metal Carbenes

“…In different catalytic systems, the [1,2]and [2,3]-rearrangements could be achieved selectively with [Cu(MeCN)4]PF6 or Rh2(oct)4 as catalyst. 23 Scheme 5 Rhodium-catalyzed asymmetric [1,2]-Stevens rearrangement of oxonium ylides for the synthesis of chiral tetrahydrofuranones 3 Catalyst-Controlled Asymmetric [1,2]-Stevens-Type Rearrangement…”

“…In different catalytic systems, the [1,2]- and [2,3]-rearrangements could be achieved selectively with [Cu(MeCN) 4 ]PF 6 or Rh 2 (oct) 4 as catalyst. 23…”