PYRYLIUM IONS AND PYRONES

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PYRYLIUM IONS AND PYRONES (chapt 7-9)
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PYRYLIUM IONS
Aromatic - Reactive Counter ion often ClO4-
c.f.
Electron deficient ring No react. with
electrophiles
No react. with radicals
Reaction with nucleophiles
(Reacts in
cycloadditions)
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Com. avail. (SciFinder) ca 170
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Reactions with nucleophiles
1,2-Add. - Ring opening!
Nu Water, alchohols, ammonia, amines,
organometallics / carbanions, Wittig reagents
hydrides
1,4-add. common on flavylium
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Reactions with nucleophiles
ANRORC (add. of Nu., Ring Opening and Ring
Closure)
More stable aromatic rings Good
yields Availability starting material
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Cycloadditions
3-oxidopyryliums
Further transformations to 7-membered rings
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Pyrones
Reactions with Electrophiles
No E-fil Ar Subst
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Reactions with Electrophiles
E-fil Ar Subst prod. by other mechanisms
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Reactions with Nucleophiles
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Reactions with Nucleophiles
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Cycloadditions
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Synthesis - Pyrylium
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Synthesis - Pyrylium
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Synthesis - Pyrones
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Natural products etc.
Flavylium
Anthocyanines - Gycosides of polyhydroxyflavyliu
m (Aglycon anthocyanidin) - Colored (red /
violet / blue) pigments, red / blue flowers,
blueberries, grapes (red wine) etc. -
Antioxidants - Polyphenols - Radical scavengers
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Natural products etc.
Kawapyrones - Isolated from Káwa - Relaxing
drug used in Polynesia
Flavonoids - Gycosides of polyhydroxyflavon -
Colored (yellow) pigments in plants -
Antioxidants Polyphenols - Radical scavengers
Rothenone -Insecticide -Parasites in rivers
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Natural products etc.

• Psoralenes
• Isolated from various plants
• -Photochemotherapy against psoriasis
• -22 cycloadd. with cytosin / thymin in DNA

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Dicoumarol -Anticoagulant - Vit K
antagonist -Sweet clower disease
Sweet clover (Melilotus officinalis)
Warfarin - Marevan

• Aflatoxines
• -From Aspergillus flavus (fungus)
• Attacks nuts etc.
• -Carcinogenic