An acyliminium ion approach towards the synthesis of β-substituted 3,4-dihydroisoquinolone propionates

A synthetic route to artificial chiral α-amino acids featuring a 3,4-dihydroisoquinolone core through a Rh(III)-catalyzed functionalization of allyl groups in chiral Ni(II) complexes

Currently, non-proteinogenic α-amino acids (α-AAs) have attracted increasing interest in bio- and medicinal chemistry. In this context, the first protocol for the asymmetric synthesis of artificial α-AAs featuring a 3,4-dihydroisoquinolone core with two stereogenic centers was successfully elaborated. A straightforward Rh(III)-catalysed C-H activation/annulation reaction of various aryl hydroxamates with a set of robust and readily available chiral Ni(II) complexes, which have allylic appendages derived from glycine (Gly), alanine (Ala) and phenylalanine (Phe), allowed incorporation of a 3,4-dihydroisoquinolone scaffold into the chiral amino acid residue. The reaction was performed in methanol and under mild conditions (at room temperature under air atmosphere), providing separable diastereomeric complexes with up to 94% total yield. The target α-AA with a 3,4-dihydroisoquinolone core in an enantiopure form was subsequently released from the obtained chiral Ni(II) complexes via an acidic decomposition in aqueous HCl, along with the recovery of the chiral auxiliary ligand.

Light-driven selective aerobic oxidation of (iso)quinoliniums and related heterocycles

Selective C1–H/C4–H carbonylation of N-methylene iminium salts, catalyzed by visible-light photoredox and oxygen in the air, has been reported. A ruthenium complex acts as a chemical switch to conduct two different reaction pathways and to afford two different kinds of products. In the absence of the ruthenium complex, the Csp²–H bonds adjacent to the nitrogen atoms are oxidized to α-lactams by the N-methyleneiminium substrates themselves as photosensitizers. In the presence of the ruthenium complex, the oxidation reaction site of quinoliniums is switched to the C4 region, resulting in the formation of 4-quinolones. The use of two transformations directly introduces oxygen into the nitrogen heterocyclic skeletons under an air atmosphere.

The selective C1–H/C4–H carbonylation of N-methyleneiminium salts catalyzed by visible-light photoredox reactions and oxygen in the air has been reported.

An efficient route to N-alkylated 3,4-dihydroisoquinolinones with substituents at the 3-position

A facile synthetic procedure for the production of N-alkylated 3,4-dihydroisoquinolinone derivatives is described. The desired products were obtained by N-alkylation of 3,3′-dimethyl-3,4-dihydroisoquinoline derivatives followed by oxidation of the resulting iminium salts. Reaction conditions for both steps were very mild and the desired cyclization products could be obtained in good yield. This strategy allows the generation of N-substituted 3,4-dihydroisoquinolinone derivatives with substituents at the 3-position.

N-Alkylated 3,4-dihydroisoquinolinone derivatives could be synthesized by N-alkylation of 3,3′-dimethyl-3,4-dihydroisoquinoline derivatives followed by oxidation of the resulting iminium salts.

The Synthesis, Structure and Reactivity of B(C6F5)3-Stabilised Amide (MNH2) Complexes of the Group 4 Metals

Treatment of the homoleptic titanium amides [Ti(NR(2))(4)] (R=Me or Et) with the Brønsted acidic reagent H(3)NB(C(6)F(5))(3) results in the elimination of one molecule of amine and the formation of the four-coordinate amidoborate complexes [Ti(NR(2))(3){NH(2)B(C(6)F(5))(3)}], the identity of which was confirmed by X-ray crystallography. The reaction with [Zr(NMe(2))(4)] proceeds similarly but with retention of the amine ligand to give the trigonal-bipyramidal complex [Zr(NMe(2))(3){NH(2)B(C(6)F(5))(3)}(NMe(2)H)]. Cyclopentadienyl (Cp) amidoborate complexes, [MCp(NR(2))(2){NH(2)B(C(6)F(5))(3)}] (M=Ti, R=Me or Et; M=Zr, R=Me) can be prepared from [MCp(NR(2))(3)] and H(3)NB(C(6)F(5))(3), and exhibit greater thermal stability than the cyclopentadienyl-free compounds. H(3)NB(C(6)F(5))(3) reacts with nBuLi or LiN(SiMe(3))(2) to give LiNH(2)B(C(6)F(5))(3), which complexes with strong Lewis acids to form ion pairs that contain weakly coordinating anions. The attempted synthesis of metallocene amidoborate complexes from dialkyl or diamide precursors and H(3)NB(C(6)F(5))(3) was unsuccessful. However, LiNH(2)B(C(6)F(5))(3) does react with the highly electrophilic reagents [MCp(2)Me(mu-Me)B(C(6)F(5))(3)] to give [MCp(2)Me(mu-NH(2))B(C(6)F(5))(3)] (M=Zr or Hf). Comparison of the molecular structures of the Group 4 amidoborate complexes reveals very similar B--N, Ti--N and Zr--N bond lengths, which are consistent with a description of the bonding as a dative interaction between an {M(L)(n)(NH(2))} fragment and the Lewis acid B(C(6)F(5))(3). Each of the structures has an intramolecular hydrogen-bonding arrangement in which one of the nitrogen-bonded hydrogen atoms participates in a bifurcated FHF interaction to ortho-F atoms.

The preparation and intra- and intermolecular addition reactions of acyclic N-acylimines: application to the synthesis of (+/-)-sertraline

Intramolecular endo-cyclization reactions of N-acyliminium ions have seen wide application for the synthesis of heterocyclic compounds. The corresponding exocyclic variant, which would provide 1-aminotetralin derivatives, for example, has little precedent. We have discovered that acyclic N-acylcarbamates can be readily reduced to the corresponding N-acylhemiaminal derivatives in high yield using DIBAL as the reducing agent. These intermediates are remarkably stable and, if desired, can be purified and stored. The acyclic N-acylhemiaminals undergo both intra- and intermolecular nucleophilic addition reactions mediated by strong Lewis acids, such as TiCl(4). Diastereoselectivity, induced either by a substituent on the newly formed ring, or by utilizing a chiral ester on the carbamic acid, was disappointingly low. This methodology was successfully applied to the synthesis of the racemic form of the marketed antidepressant sertraline.