Stereocontrolled Syntheses of Seven‐Membered Carbocycles by Tandem Allene Aziridination/[4+3] Reaction

Abstract

A tandem allene aziridination/[4+3]/reduction sequence converts simple homoallenic sulfamates to densely functionalized aminated cycloheptenes, where the relative stereochemistry at five contiguous asymmetric centers can be controlled through the choice of the solvent and the reductant. The products resulting from this chemistry can be readily transformed into complex molecular scaffolds that contain up to seven contiguous stereocenters.

Enantioselective Functionalization of Enamides at the β‐Carbon Center with Indoles

“…[4] We envisioned that stereoablative ionization of this starting material with ac hiral Brønsted acid should produce unsymmetric 2-amidoallyl cation 5a. [5] In the presence of the readily dissociated triflate counteranion, this intermediate has been shown to undergo nucleophilic capture exclusively at the less substituted a'-carbon atom to furnish a'-functionalized enamides 6. [6] Inspired by this work, we proposed that the activation of substrate 4 with ac hiral Brønsted acid invokes am uch tighter ion-pair interaction [7] between the emerging 2-amidoallyl cation and the bulky chiral anion.…”

Synthesis and applications of methyleneaziridines

“…61 The examples of intermolecular [4 + 3] reactions were reported by the Schomaker group. 84 Based on their previous research on bicyclic MAs, a tandem allene aziridination/[4 + 3]/ reduction sequence was skillfully designed and successfully utilized to convert homoallenic sulfamates into densely functionalized aminated cycloheptenes. As shown in Scheme 59, In 2017, the Schomaker group reported an impressive [3 + 1] ring expansion of bicyclic MAs, in combination with Rhsupported carbenes, to deliver tri-and tetra-substituted methylene azetidines.…”

Scalable Synthesis of Esp and Rhodium(II) Carboxylates from Acetylacetone and RhCl3·xH2O

“…We questioned whether Rh 2 esp 2 ( 1 ) could be prepared directly from RhCl 3 · x H 2 O ( 8 ) and esp ( 2 ), similarly to the simpler rhodium­(II) carboxylates 7a and b . ,,,− In the classic synthesis by Wilkinson of Rh 2 (OAc) 4 ( 7a ; Scheme C), rhodium­(III) chloride 8 is reduced by ethanol in the presence of 90–120 equiv of the acetic acid ligand and small amounts of sodium acetate . In fact, acidic conditions are commonly used to reduce rhodium­(III) using alcohols ( E 0 {Rh­(III)–Rh­(II)} = 0.7 V vs SHE), , and this principle has not been questioned since the early work by Wilkinson .…”

“…Given the particular chelate structure of the ligand esp ( 2 ), we interrogated whether it was possible to obtain with the same method other privileged monocarboxylate rhodium­(II) catalysts, which are relevant in a wide range of carbene and nitrene insertion reactions. − To our delight, using only marginal excess of the simple pivalic or octanoic acids under similar conditions, the corresponding complexes 15 and 16 were also produced (Scheme ). Even the bulky triphenylacetic acid yields the congested Rh 2 TPA 4 catalyst ( 17 ) at significantly lower temperature than through current ligand metathesis.…”