Accessing simply-substituted 4-hydroxytetrahydroisoquinolines via Pomeranz-Fritsch-Bobbitt reaction with non-activated and moderately-activated systems

Marco Mottinelli, Mathew P. Leese, Barry V.L. Potter

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

Background: 1,2,3,4-Tetrahydroisoquinolines (THIQs) are common motifs in alkaloids and in medicinal chemistry. Synthetic access to THIQs via the Pomeranz-Fritsch-Bobbit (PFB) methodology using mineral acids for deactivated, electron-poor aromatic systems, is scarcely represented in the literature. Here, the factors controlling the regiochemical outcome of cyclization are evaluated. Results: A double reductive alkylation was telescoped into a one-pot reaction delivering good to excellent yields of desired aminoacetals for cyclization. Cyclization of activated systems proceeded smoothly under standard PFB conditions, but for non-activated systems the use of HClO4 alone was effective. When cyclization was possible in both para- and ortho-positions to the substituent, 7-substituted derivatives were formed with significant amounts of 5-substituted byproduct. The formation of the 4-hydroxy-THIQs vs the 4-methoxy-THIQ products could be controlled through modification of the reaction concentration. In addition, while a highly-activated system exclusively cyclized to the indole, this seems generally highly disfavored. When competition between 6-and 7-ring formation was investigated in non-activated systems, 5,7,8,13-tetrahydro-6,13-methanodibenzo[c,f]azonine was exclusively obtained. Furthermore, selective ring closure in the para-position could be achieved under standard PFB conditions, while a double ring closure could be obtained utilizing HClO4. Conclusion: Reactivity differences in aminoacetal precursors can be employed to control cyclization using the PFB methodology. It is now possible to select confidently the right conditions for the synthesis of N-aryl-4-hydroxy-1,2,3,4-tetrahydroisoquinolines.

Original languageEnglish
Pages (from-to)1871-1879
Number of pages9
JournalBeilstein Journal of Organic Chemistry
Volume13
DOIs
Publication statusPublished - 6 Sep 2017

Fingerprint

Tetrahydroisoquinolines
Cyclization
Alkylation
Alkaloids
Minerals
Byproducts
Derivatives
Acids
Electrons

Keywords

  • Cyclization
  • Pomeranz-Fritsch
  • Steroidomimetic
  • Synthesis
  • Tetrahydroisoquinoline

ASJC Scopus subject areas

  • Organic Chemistry

Cite this

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title = "Accessing simply-substituted 4-hydroxytetrahydroisoquinolines via Pomeranz-Fritsch-Bobbitt reaction with non-activated and moderately-activated systems",
abstract = "Background: 1,2,3,4-Tetrahydroisoquinolines (THIQs) are common motifs in alkaloids and in medicinal chemistry. Synthetic access to THIQs via the Pomeranz-Fritsch-Bobbit (PFB) methodology using mineral acids for deactivated, electron-poor aromatic systems, is scarcely represented in the literature. Here, the factors controlling the regiochemical outcome of cyclization are evaluated. Results: A double reductive alkylation was telescoped into a one-pot reaction delivering good to excellent yields of desired aminoacetals for cyclization. Cyclization of activated systems proceeded smoothly under standard PFB conditions, but for non-activated systems the use of HClO4 alone was effective. When cyclization was possible in both para- and ortho-positions to the substituent, 7-substituted derivatives were formed with significant amounts of 5-substituted byproduct. The formation of the 4-hydroxy-THIQs vs the 4-methoxy-THIQ products could be controlled through modification of the reaction concentration. In addition, while a highly-activated system exclusively cyclized to the indole, this seems generally highly disfavored. When competition between 6-and 7-ring formation was investigated in non-activated systems, 5,7,8,13-tetrahydro-6,13-methanodibenzo[c,f]azonine was exclusively obtained. Furthermore, selective ring closure in the para-position could be achieved under standard PFB conditions, while a double ring closure could be obtained utilizing HClO4. Conclusion: Reactivity differences in aminoacetal precursors can be employed to control cyclization using the PFB methodology. It is now possible to select confidently the right conditions for the synthesis of N-aryl-4-hydroxy-1,2,3,4-tetrahydroisoquinolines.",
keywords = "Cyclization, Pomeranz-Fritsch, Steroidomimetic, Synthesis, Tetrahydroisoquinoline",
author = "Marco Mottinelli and Leese, {Mathew P.} and Potter, {Barry V.L.}",
year = "2017",
month = "9",
day = "6",
doi = "10.3762/bjoc.13.182",
language = "English",
volume = "13",
pages = "1871--1879",
journal = "Beilstein Journal of Organic Chemistry",
issn = "1860-5397",
publisher = "Beilstein-Institut Zur Forderung der Chemischen Wissenschaften",

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TY - JOUR

T1 - Accessing simply-substituted 4-hydroxytetrahydroisoquinolines via Pomeranz-Fritsch-Bobbitt reaction with non-activated and moderately-activated systems

AU - Mottinelli, Marco

AU - Leese, Mathew P.

AU - Potter, Barry V.L.

PY - 2017/9/6

Y1 - 2017/9/6

N2 - Background: 1,2,3,4-Tetrahydroisoquinolines (THIQs) are common motifs in alkaloids and in medicinal chemistry. Synthetic access to THIQs via the Pomeranz-Fritsch-Bobbit (PFB) methodology using mineral acids for deactivated, electron-poor aromatic systems, is scarcely represented in the literature. Here, the factors controlling the regiochemical outcome of cyclization are evaluated. Results: A double reductive alkylation was telescoped into a one-pot reaction delivering good to excellent yields of desired aminoacetals for cyclization. Cyclization of activated systems proceeded smoothly under standard PFB conditions, but for non-activated systems the use of HClO4 alone was effective. When cyclization was possible in both para- and ortho-positions to the substituent, 7-substituted derivatives were formed with significant amounts of 5-substituted byproduct. The formation of the 4-hydroxy-THIQs vs the 4-methoxy-THIQ products could be controlled through modification of the reaction concentration. In addition, while a highly-activated system exclusively cyclized to the indole, this seems generally highly disfavored. When competition between 6-and 7-ring formation was investigated in non-activated systems, 5,7,8,13-tetrahydro-6,13-methanodibenzo[c,f]azonine was exclusively obtained. Furthermore, selective ring closure in the para-position could be achieved under standard PFB conditions, while a double ring closure could be obtained utilizing HClO4. Conclusion: Reactivity differences in aminoacetal precursors can be employed to control cyclization using the PFB methodology. It is now possible to select confidently the right conditions for the synthesis of N-aryl-4-hydroxy-1,2,3,4-tetrahydroisoquinolines.

AB - Background: 1,2,3,4-Tetrahydroisoquinolines (THIQs) are common motifs in alkaloids and in medicinal chemistry. Synthetic access to THIQs via the Pomeranz-Fritsch-Bobbit (PFB) methodology using mineral acids for deactivated, electron-poor aromatic systems, is scarcely represented in the literature. Here, the factors controlling the regiochemical outcome of cyclization are evaluated. Results: A double reductive alkylation was telescoped into a one-pot reaction delivering good to excellent yields of desired aminoacetals for cyclization. Cyclization of activated systems proceeded smoothly under standard PFB conditions, but for non-activated systems the use of HClO4 alone was effective. When cyclization was possible in both para- and ortho-positions to the substituent, 7-substituted derivatives were formed with significant amounts of 5-substituted byproduct. The formation of the 4-hydroxy-THIQs vs the 4-methoxy-THIQ products could be controlled through modification of the reaction concentration. In addition, while a highly-activated system exclusively cyclized to the indole, this seems generally highly disfavored. When competition between 6-and 7-ring formation was investigated in non-activated systems, 5,7,8,13-tetrahydro-6,13-methanodibenzo[c,f]azonine was exclusively obtained. Furthermore, selective ring closure in the para-position could be achieved under standard PFB conditions, while a double ring closure could be obtained utilizing HClO4. Conclusion: Reactivity differences in aminoacetal precursors can be employed to control cyclization using the PFB methodology. It is now possible to select confidently the right conditions for the synthesis of N-aryl-4-hydroxy-1,2,3,4-tetrahydroisoquinolines.

KW - Cyclization

KW - Pomeranz-Fritsch

KW - Steroidomimetic

KW - Synthesis

KW - Tetrahydroisoquinoline

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UR - http://dx.doi.org/10.3762/bjoc.13.182

U2 - 10.3762/bjoc.13.182

DO - 10.3762/bjoc.13.182

M3 - Article

VL - 13

SP - 1871

EP - 1879

JO - Beilstein Journal of Organic Chemistry

JF - Beilstein Journal of Organic Chemistry

SN - 1860-5397

ER -