- Allyl, methallyl, prenyl, and methylprenyl ethers as protected alcohols: Their selective cleavage with diphenyldisulfone under neutral conditions
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Diphenyldisulfone is a mild and efficient reagent for selective cleavage of methylprenyl (2,3-dimethylbut-2-en-1-yl), prenyl (3-methylbut-2-en1-yl), and methallyl (2-methylallyl) ethers. These reaction conditions are compatible with the presence of other protecting groups such as acetals, acetates, and allyl, benzyl, and TBDMS ethers. Exposure of 2,3-dimethylbut-2-en-1-yl and 3-methylbut-2-en1-yl ethers to diphenyldisulfone led to the formation of 2,3-dimethylbuta-1,3-diene and isoprene, respectively. 2-Methylallyl ethers undergo isomerization to 2-methylpropenyl ethers, which are easily hydrolyzed into the corresponding free alcohols and isobutyraldehyde.
- Markovic, Dean,Vogel, Pierre
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p. 2693 - 2696
(2007/10/03)
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- The prenyl group: A versatile hydroxy protecting group, removable chemoselectively under mild conditions
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Iodine in dichloromethane (in the presence of 3? molecular sieves for acid-sensitive substrates) and 2,3-dichloro-5,6-dicyanoquinone (DDQ) in dichloromethane-water (9:1) are mild and efficient methods to cleave prenyl ethers. These reaction conditions are compatible with the presence of other protecting groups such as acetals, acetates, allyl, benzyl and TBDPS groups. Exposure of aryl prenyl ethers to iodine led to the formation of 3-iodo-2,2-dimethylchroman derivatives in acceptable yields via a tandem Friedel-Crafts/iodocyclization reactions. Facile one-step transformation of two iodinated dimethylchroman derivatives allowed the synthesis of natural flavanoids among them: zanthoxylol, an anti-sickling agent.
- Vatèle, Jean-Michel
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p. 5689 - 5698
(2007/10/03)
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