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  • Which intramolecular substitution products are listed for synthesizing three-membered rings?

    • Oxiran (epoxide)
    • Aziridin
    synthesis 3-ring

  • Which named procedure converts a precursor into an epoxide (oxiran) in the notes?

    • Wartz -> Oxiran / Epoxide
    epoxide wartz

  • Which named procedure converts a precursor into an aziridine in the notes?

    • Wenker -> Aziridin
    aziridine wenker

  • Which reagents are specified for Mitsunobu-cyclisation to form three-membered rings?

    • PPh3 and DEAD
    mitsunobu reagents

  • What two general transformations are listed for making three-membered heterocycles?

    • Epoxidation
    • Aziridination
    3-ring transformations

  • How can three-membered rings be synthesized from carbonyls or imines according to the notes?

    • Using Sulfur-ylid
    sulfur-ylid 3-ring

  • Name two approaches listed for synthesizing four-membered rings.

    • Intramolecular substitution with haloalcohols/haloamines
    • [2+2] cycloaddition
    4-ring methods

  • Which photochemical reaction is listed for making four-membered rings from an alkene and a carbonyl?

    • Paterno-Büchi-Reaktion (Alken + Carbonyl)
    paterno-büchi photochemistry

  • Which reaction combining a keten and an imine is listed for four-membered ring synthesis?

    • Staudinger-Synthese (Keten + Imine)
    staudinger 4-ring

  • List the general routes given for synthesizing five-membered rings.

    • Cyclisation
    • (3+2) Cycloaddition
    5-ring cycloaddition

  • Which 1,3-dipoles or related species are listed for (3+2) cycloadditions to form five-membered rings?

    • Azide
    • Nitriloxide
    • Nitrone
    • Azomethin-ylide
    dipole 5-ring

  • Which two general methods are listed for synthesizing six-membered rings?

    • Cyclisation
    • Hetero-Diels-Alder
    6-ring methods

  • What reagents form pyrrole in the Paal–Knorr synthesis?

    • Ammoniak/primary amines and 1,4-dicarbonyl
    paal-knorr pyrrole heterocycle

  • What reagent combination gives furan in the Paal–Knorr synthesis?

    • 1,4-dicarbonyl
    paal-knorr furan heterocycle

  • What is required to synthesize thiophene via Paal–Knorr?

    • 1,4-dicarbonyl and a Sulfur source (P2S5 or Lawesson-Reagent)
    paal-knorr thiophene heterocycle

  • Which starting materials are used in the Knorr synthesis to make pyrrole?

    • alpha-Aminoketone and beta-dicarbonyl
    knorr pyrrole heterocycle

  • Which reagents are paired in the Van Leusen method to form pyrrole?

    • Imines and TosMIC
    van-leusen pyrrole heterocycle

  • What are the key reagents for the Fischer synthesis of a heterocycle with one heteroatom and two rings (one 5-ring)?

    • Arylhydrazin and Aldehyde/ketone
    fischer heterocycle synthesis

  • What starting materials and catalyst are used in the Castro synthesis for a fused heterocycle?

    • o-Halogenaniline, Alkine, Cu-Catalyst
    castro heterocycle copper

  • What single substrate is listed for the Reissert synthesis in this overview?

    • o-Nitrotoluol
    reissert heterocycle

  • Which reagents and catalyst are used in the Mori–Ban–Heck synthesis?

    • o-Halogenaniline, Alkene, Pd-Catalyst
    mori-ban-heck heterocycle palladium

  • What three components form 1,3-azoles in the Debus–Radiszewski synthesis?

    • 1,2-dicarbonyl, aldehyde, 2 Ammoniak/primary amines
    debus-radiszewski 1,3-azoles heterocycle

  • What reagents are required for the Hantzsch-type thiazole synthesis from halogencarbonyls?

    • alpha-halogencarbonyl and Thioamide
    hantzsch thiazole halogencarbonyl

  • In Van Leusen routes to oxazoles and imidazoles, which partners are used with TosMIC?

    • Aldehyde (Oxazoles) / Amine (Imidazole) with Base (K2CO3/NaOMe)
    van-leusen tosmic azoles

  • What substrates form pyrazole according to the overview for 1,2-azoles?

    • 1,3-dicarbonyl and hydrazine
    pyrazole 1,2-azoles hydrazine

  • Which reagents are listed to synthesize 'Isoxazol'?

    • 1,3-dicarbonyl
    • hydroxylamine
    isoxazol reagents

  • Which dipolar cycloaddition pair is given to form 'Isoxazol'?

    • Nitriloxid + Alkine
    isoxazol cycloaddition

  • Which dipolar cycloaddition pair is given to form 'Pyrazol'?

    • Diazomethan + Alkine
    pyrazol cycloaddition

  • Which reagents are used in the Huisgen-Alky-Azid cycloaddition to make 1,2,3-triazole?

    • Azid + Alkine
    triazole huisgen

  • What are the components of the Hantzsch synthesis listed for a one-heteroatom six-membered ring?

    • 2 beta-dicarbonyl
    • aldehyde
    • NH3/Ammoniumacetate
    hantzsch synthesis

  • Which three-component assembly is listed as coming from 1,5-dicarbonyl and NH3?

    • From 1,5-dicarbonyl and NH3
    hantzsch alternative

  • Which [2+2+2] cycloaddition partners are listed to build a one-heteroatom six-membered ring?

    • 2 Alkines + 1 Nitrile
    cycloaddition 2+2+2

  • Which [4+2] cycloaddition partners are listed for making a one-heteroatom six-membered ring?

    • Diels–Alder (general [4+2] cycloaddition)
    diels-alder 4+2

  • Which starting heterocycles are listed as precursors to one-heteroatom six-membered rings with alkine/alkene?

    • Oxazoles + Alkine/Alkene
    oxazole ring-formation

  • Which starting heterocycle is listed to form six-membered rings with electron-rich alkines?

    • Triazines + electron rich alkines
    triazine synthesis

  • What are the reagents for the Combes synthesis to form one-heteroatom, two fused six-rings?

    • aniline + 1,3-dicarbonyl
    combes synthesis

  • What starting materials does the Friedländer synthesis use for fused six-membered ring systems?

    • o-Aminobenzaldehyd + Carbonyl
    friedlander synthesis

  • What is the starting material listed for the Pictet-Gams synthesis?

    • beta-hydroxy-beta-phenylethylamide
    pictet-gams synthesis

  • Which reagents are given to synthesize 'Pyridazin'?

    • 1,4-dicarbonyls + hydrazine
    pyridazin reagents

  • Which cycloaddition is listed as an alternative route to 'Pyridazin'?

    • [4+2] Cycloaddition of tetrazines with alkines
    pyridazin cycloaddition

  • Which reagents are listed to form 'Pyrimidin'?

    • 1,3-dicarbonyls + Amidin/Urea
    pyrimidin reagents

  • Which reagents are listed to form 'Pyrazin'?

    • 1,2-dicarbonyls + 1,2-diamines
    pyrazin reagents

  • What starting material is mentioned for the syntheses?

    2-aminoketones

    precursor

  • Which target molecule class is specified under 'Synthesis'?

    Purine

    purine

  • Which two topics are noted as 'just need to know what its about'?

    • Eintopfreaktion
    • präbiotische synthesen
    topics

  • Name three of the important reactions listed.

    • Vilsmeier Haack
    • Pictet-Spengler Reaction
    • Dipolar cycloaddition
    reactions

  • List all important reactions mentioned.

    • Vilsmeier Haack
    • Pictet-Spengler Reaction
    • Dipolar cycloaddition
    • Suzuki miyaura
    • Benzoinkondensation
    • Ziegler-reaktion
    • Chichibabin-reaction
    reactions named

  • Is 'Dipolar cycloaddition' included among the important reactions?

    Yes

    reactions
学习笔记

Overview

Concise guide to common synthetic methods for making 3–6 membered carbocycles and heterocycles, plus selected named reactions used to assemble heteroatom-containing rings.

General strategies for small-ring formation (3–4 members)

  • 3-membered rings (epoxides, aziridines)
  • Intramolecular substitution: haloalcohols/haloamines cyclize to epoxides/aziridines.
  • Wartz → Oxiran / Epoxide: listed as a route to epoxides (see course notes).
  • Wenker → Aziridin: specific transformation to aziridines.
  • Mitsunobu cyclisation: intramolecular Mitsunobu (PPh3 + DEAD) can form strained rings from alcohols and nucleophiles.
  • Direct addition: epoxidation of alkenes; aziridination of alkenes with nitrenoid sources.

  • Sulfur ylides: convert carbonyls/imines into epoxides/aziridines via ylides.

  • 4-membered rings (cyclobutanes, azetidines, oxetanes)

  • Intramolecular substitution of suitably spaced haloalcohols/haloamines.
  • [2+2] Cycloaddition: photochemical or thermal [2+2] between alkenes or ketenes and alkenes.
  • Paterno–Büchi: carbonyl + alkene → oxetane (photochemical [2+2]).
  • Staudinger-type: ketene + imine → β-lactam (a formal [2+2] addition).

Strategies for 5-membered rings (general)

  • Main pathways:
  • Intramolecular cyclisation of linear precursors.
  • (3+2) Cycloadditions (dipolar cycloadditions) to build 5-membered frameworks.

  • Formation from functional group interconversion (azides, nitrones, nitrile oxides, azomethine ylides).

  • Typical dipoles and partners:

  • Azides → 1,2,3-triazoles (via cycloaddition with alkynes).
  • Nitrile oxides → isoxazoles (with alkynes).
  • Nitrones → isoxazolidines / related 5-membered products.
  • Azomethine ylides → pyrrolidine frameworks via 1,3-dipolar cycloaddition.

Strategies for 6-membered rings (general)

  • Cyclisation of appropriate 1,5- or 1,6- precursors.
  • Hetero-Diels–Alder (4+2): builds oxygen- or nitrogen-containing six-membered rings.
  • [2+2+2] cycloadditions (for N-containing aromatics from alkynes + nitriles) often used for heteroaromatics.

One heteroatom in a 5-membered ring (specific named syntheses)

  • Paal–Knorr synthesis
  • Pyrroles: primary amine or ammonia + 1,4-dicarbonyl.
  • Furans: acid-catalyzed cyclization of 1,4-dicarbonyls.
  • Thiophenes: 1,4-dicarbonyl + sulfur source (P2S5 or Lawesson reagent).

  • Alternative: build 1,4-dicarbonyls from alkynes via Michael addition or Stetter reaction (NHC-catalyzed).

  • Knorr synthesis

  • Pyrroles from an α-amino ketone plus a β-dicarbonyl compound.

  • Van Leusen

  • Pyrrole formation using TosMIC and imines (or related partners).

One heteroatom, fused/bi-cyclic 5-ring systems (routes)

  • Fischer synthesis: arylhydrazine + carbonyl → indole-type chemistry (for fused 5-rings).
  • Castro, Reissert, Mori–Ban–Heck: cross-coupling or annulation strategies starting from o-halogen anilines, alkynes, alkenes or nitroarenes to build fused N-heterocycles.

1,3-Azoles (oxazoles, thiazoles, imidazoles)

  • Debus–Radiszewski: 1,2-dicarbonyl + aldehyde + ammonia/primary amine → imidazole core.
  • Hantzsch-type (thiazole): α-halo carbonyl + thioamide → thiazole.
  • Van Leusen (TosMIC): aldehyde + TosMIC → oxazole (or with amine → imidazole) using base (K2CO3 or NaOMe).

1,2-Azoles and related (pyrazoles, isoxazoles)

  • From 1,3-dicarbonyls: condensation with hydrazine → pyrazoles.
  • Isoxazoles: 1,3-dicarbonyl + hydroxylamine forms isoxazoles.
  • Dipolar cycloadditions:
  • Nitrile oxides + alkynes → isoxazoles.
  • Diazomethane + alkynes → pyrazoles (via 1,3-dipolar addition).

1,2,3-Triazoles

  • Huisgen 1,3-dipolar cycloaddition: azide + alkyne → 1,2,3-triazole (thermal or Cu(I)-catalyzed click variant).

One heteroatom in a 6-membered ring (methods)

  • Hantzsch synthesis: two β-dicarbonyls + aldehyde + NH3 / ammonium acetate → dihydropyridine → pyridine derivatives after oxidation.
  • From 1,5-dicarbonyl + NH3: direct cyclisation to 6-membered N-heterocycles.
  • [2+2+2] cycloadditions: two alkynes + nitrile → substituted pyridines.
  • Diels–Alder (4+2): hetero-Diels–Alder builds oxygen- or nitrogen-containing six-membered rings.
  • From azoles/triazines: ring transformation or cycloaddition of electron-rich alkynes/alkenes to give 6-membered heterocycles.

One heteroatom, two fused 6-rings (bicyclic N-heterocycles)

  • Combes synthesis: aniline + 1,3-dicarbonyl → quinoline derivatives.
  • Friedländer synthesis: o-aminobenzaldehyde + ketone → quinoline cores.
  • Pictet–Gams: cyclization of β-hydroxy-β-phenylethylamide to form tetrahydroisoquinoline frameworks.

Two heteroatoms in one ring (diazines and related)

  • Pyridazine (1,2- or 1,6- diazine)
  • From 1,4-dicarbonyls + hydrazine.

  • Also accessible by [4+2] cycloaddition of tetrazines with alkynes (retro-[4+2] extrusion of N2).

  • Pyrimidine

  • From 1,3-dicarbonyls condensed with amidines or urea-type N-sources.

  • Pyrazine

  • From 1,2-dicarbonyls + 1,2-diamines or from 2-aminoketones.

Purines and polycycles

  • Purine syntheses often involve multi-step ("Eintopf") or prebiotic-type one-pot assemblies; course note: know concept and general assembly logic rather than every variant.

Other named reactions and useful tools (select list)

  • Vilsmeier–Haack formylation
  • Pictet–Spengler cyclization (β-arylethylamines with aldehydes)
  • Dipolar cycloaddition methods for 5-membered rings
  • Suzuki–Miyaura cross-coupling for assembling substituted rings
  • Benzoin condensation for building α-hydroxy ketones
  • Ziegler-type reactions (polyolefin or metal-mediated transformations)
  • Chichibabin reaction (nucleophilic aromatic substitution on pyridines)

Practical tips for studying ring syntheses

  • Group methods by ring size and by the number/type of heteroatoms to simplify memorization.
  • Learn one representative mechanism per named reaction (key intermediates and driving force).
  • Recognize common building blocks: 1,3- and 1,4-dicarbonyls, alkynes, azides, nitrile oxides, hydrazines, TosMIC.
  • Remember common catalysts/reagents associated with names (e.g., PPh3/DEAD for Mitsunobu, TosMIC + base for Van Leusen, NH3/acetate for Hantzsch).

Quick reference: common ring-building motifs

  • 3-membered: intramolecular substitution, epoxidation/aziridination, sulfur ylides.
  • 4-membered: [2+2] cycloaddition, Paterno–Büchi, ketene + imine (β-lactams).
  • 5-membered (hetero): Paal–Knorr, Knorr, Van Leusen, (3+2) dipolar cycloadditions.
  • 6-membered (hetero): Hantzsch, Diels–Alder, [2+2+2] cycloadditions, ring transformations.