Enantioselective Addition of Vinylzinc Reagents to 3,4-Dihydroisoquinoline N-Oxide

Enantioselective Synthesis of 1-Aryl Tetrahydroisoquinolines by the Rhodium-Catalyzed Reaction of 3,4-Dihydroisoquinolinium Tetraarylborates

The 1-aryl tetrahydroisoquinolines (1-aryl THIQs) are omnipresent in biologically active molecules. Here we report on the direct asymmetric synthesis of these valuable compounds via the reaction of 3,4-dihydroisoquinolinium tetraarylborates. The dual roles of anionic tetraarylborates, which function as both prenucleophiles and stabilizers of 3,4-dihydroisoquinolinium cations, enable this rhodium(I)-catalyzed protocol to convergently provide enantioenriched 1-aryl THIQs in good yields (≤95%) with ≤97% ee, as demonstrated by the formal synthesis of (-)-solifenacin and the facile synthesis of (-)-Cryptostyline I.

Asymmetric Synthesis of C1-Chiral THIQs with Imines in Isoquinoline Rings

Tetrahydroisoquinoline (THIQ) scaffolds are important structural units that widely exist in a variety of natural alkaloids and synthetic analogues. Asymmetric synthesis of C1-chiral THIQ is of particular importance due to its significant pharmaceutical, agrochemical, and other biological activities, and the usually distinct bioactivities exhibited by the two enantiomers. In this review, we highlight the significant advances achieved in this field, present recent asymmetric synthesis with imines in isoquinoline rings ordered according to the sequence of various substrate types. New strategies could be inspired and more types of substrates need further development.

1 Introduction

2 Catalytic Asymmetric Reaction of Dihydroisoquinolines

2.1 Asymmetric Reactions of 3,4-Dihydroisoquinolines

2.2 Asymmetric Reactions of Dihydroisoquinolinium Salts

2.3 Asymmetric Reactions of C,N-Cyclic N′-Acyl Azomethine Imines

2.3.1 NED [3+2] Cycloaddition of C,N-Cyclic N′-Acyl Azomethine Imines

2.3.2 IED [3+2] Cycloaddition of C,N-Cyclic N′-Acyl Azomethine Imines

2.3.3 [3+3] Cycloaddition of C,N-Cyclic N′-Acyl Azomethine Imines

2.3.4 [4+3] Cycloaddition of C,N-Cyclic N′-Acyl Azomethine Imines

2.3.5 Asymmetric Addition Reactions to C,N-Cyclic N′-Acyl Azomethine Imines

2.4 Asymmetric Reactions of C,N-Cyclic Nitrones

3 Catalytic Asymmetric Mannich Reactions of Isoquinolines

4 Conclusions and Perspectives

Rhodium-Catalyzed Enantioselective Alkenylation of Cyclic Ketimines: Synthesis of Multifunctional Chiral α,α-Disubstituted Allylic Amine Derivatives

By employing a simple open-chain chiral phosphite-olefin ligand, a highly enantioselective rhodium-catalyzed alkenylation of 1,2,5-thiadiazole 1,1-dioxide-type cyclic ketimines with diverse vinylboronic acids was achieved under mild conditions at room temperature. This protocol provides an efficient and practical access to multifunctional α,α-disubstituted chiral allylic amines bearing quaternary stereocenters in high yields (up to 99%) with good to excellent ee's (up to 99%).

Asymmetric Synthesis of Isoquinoline Alkaloids: 2004-2015

In the past decade, the asymmetric synthesis of chiral nonracemic isoquinoline alkaloids, a family of natural products showing a wide range of structural diversity and biological and pharmaceutical activity, has been based either on continuation or improvement of known traditional methods or on new, recently developed, strategies. Both diastereoselective and enantioselective catalytic methods have been applied. This review describes the stereochemically modified traditional syntheses (the Pictet-Spengler, the Bischler-Napieralski, and the Pomeranz-Fritsch-Bobbitt) along with strategies based on closing of the nitrogen-containing ring B of the isoquinoline core by the formation of bonds between C₁-N₂, N₂-C₃, C₁-N₂/N₂-C₃, and C₁-N₂/C₄-C_4a atoms. Methods involving introduction of substituents at the C1 carbon of isoquinoline core along with syntheses applying various biocatalytic techniques have also been reviewed.

Synthesis of Tetrahydroisoquinoline Alkaloids and Related Compounds through the Alkylation of Anodically Prepared α-Amino Nitriles

α-Amino nitrile 2a was conveniently prepared in two individual steps from chiral hexafluorophosphate salt isoquinolinium (-)-8b including anodic cyanation as an efficient means to activate the sp(3) C1-H bond of the THIQ nucleus. The lithiation of 2a was carried out in THF at -80 °C in the presence of LDA to produce a stable α-amino carbanion which was condensed on a large variety of alkyl halides. The resulting quaternary α-amino nitriles were subjected to a stereoselective reductive decyanation in ethanol in the presence of NaBH4 as the hydride donor to yield N-Boc-1-alkyl-THIQs (+)-10a-g in up to 97:3 er's after removal of the chiral auxiliary group. Examination of the ORTEP view of THIQ (+)-1f revealed that the newly created stereogenic center had an absolute S configuration. Likewise, (-)-xylopinine was synthesized in four workup steps in an overall 63% yield from α-amino nitrile (+)-2b. In this process, crystallization of an enantioenriched mixture (90:10) of (-)-norlaudanosine with 1 equiv of (-)-N-acetyl-l-leucine afforded the leucinate salt (+)-13 (99:1 dr). Similarly, (+)-salsolidine was displaced from its (-)-DBTA salt (-)-12 in 99:1 er, which was determined by proton and carbon NMR spectroscopy in the presence of thiophosphinic acid (+)-14 as the chiral solvating agent.

Novel strategies for catalytic asymmetric synthesis of C1-chiral 1,2,3,4-tetrahydroisoquinolines and 3,4-dihydrotetrahydroisoquinolines

This review summarizes recent progress in catalytic asymmetric construction of 1,2,3,4-tetrahydroisoquinolines and 3,4-dihydroisoquinolines, among the most important “privileged scaffolds”.

Organocatalytic enantioselective synthesis of 1-vinyl tetrahydroisoquinolines through allenamide activation with chiral Brønsted acids

In this paper we present a new approach for the realization of tetrahydroisoquinoline scaffolds via stereoselective proto-activation of suitable allenamide precursors.

Asymmetric synthesis of tetrahydroquinolines through supramolecular organocatalysis

Functionalized chiral tetrahydroquinolines were synthesized through supramolecular organocatalysis using quinidine-NH-thiourea 3c/l-phenylalanine 4i followed by reductive amination from the simple substrates.

Enantioselective double manipulation of tetrahydroisoquinolines with terminal alkynes and aldehydes under copper(I) catalysis

Tetrahydroisoquinoline alkaloids with a C1 stereogenic center are a common unit in many natural and non-natural compounds of biological importance. Herein we describe a novel Cu(I) -catalyzed highly chemo- and enantioselective synthesis of chiral tetrahydroisoquinoline-alkaloid derivatives from readily available unsubstituted tetrahydroisoquinolines, aldehydes, and terminal alkynes in the presence of the ligand (R,R)-N-pinap. This synthetic operation installs two substituents in the 1- and 2-positions.

Controlling stereoselectivity by enzymatic and chemical means to access enantiomerically pure (1S,3R)-1-benzyl-2,3-dimethyl-1,2,3,4-tetrahydroisoquinoline derivatives

A chemoenzymatic strategy for the synthesis of enantiomerically pure novel alkaloids (1S,3R)-1-benzyl-2,3-dimethyl-1,2,3,4-tetrahydroisoquinolines is presented. The key steps are the biocatalytic stereoselective reductive amination of substituted 1-phenylpropan-2-one derivatives to yield chiral amines employing microbial ω-transaminases, and the diastereoselective reduction of a Bischler–Napieralski imine intermediate by catalytic hydrogenation in the presence of palladium on charcoal, leading exclusively to the desired cis-isomer.

Biocatalytic organic synthesis of optically pure (S)-scoulerine and berbine and benzylisoquinoline alkaloids

A chemoenzymatic approach for the asymmetric total synthesis of the title compounds is described that employs an enantioselective oxidative C-C bond formation catalyzed by berberine bridge enzyme (BBE) in the asymmetric key step. This unique reaction yielded enantiomerically pure (R)-benzylisoquinoline derivatives and (S)-berbines such as the natural product (S)-scoulerine, a sedative and muscle relaxing agent. The racemic substrates rac-1 required for the biotransformation were prepared in 4-8 linear steps using either a Bischler-Napieralski cyclization or a C1-Cα alkylation approach. The chemoenzymatic synthesis was applied to the preparation of fourteen enantiomerically pure alkaloids, including the natural products (S)-scoulerine and (R)-reticuline, and gave overall yields of up to 20% over 5-9 linear steps.