2- Phenyl sultams, synthesis

Acyclic dienes bearing Oppolzer s sultam auxiliary 261 have been utilized in the synthesis of functionalized 1,4-dihydronaphthalenes <05JA15028>. Cycloaddition of dienes 261 with benzynes, generated from 2(trimethylsilyl)phenyl triflate 263 using cesium fluoride, provides cycloadducts 263 with excellent diastereoselectivities. 

The a-methyltoluene-2,o -sultam auxiliary is also displaced by a variety of dilithiated alkyl phenyl sulfones. This unique procedure provides direct access to synthetically useful fi-o o sul-fones which may he further functionalized or simply subjected to reductive desulfonation to give alkyl ketones. A particularly striking use of this method is the preparation of p-oxo sulfone 8, a key intermediate in a concise synthesis of (—)-semicorole (eq 5). Remarkably, the MeCLi2S02Ph reagent attacks selectively the C(4)-imide C=0 group in preference to the C(6)-ester C=0 group and no epimerization occurs at C(3) or C(F). 

The benzyne created from 2-(trimethylsilyl)phenyl triflate was used in a highly diastereoselective aryne Diels-Alder reaction with a diene bearing Oppolzer s sultam. This approach to cis-functionalized 1,4-dihydronaphthalenes was reportedly the first aryne Diels-Alder reaction to provide enantioenriched cyclo-adducts. An unusual route to /3-aminoketones involves the treatment of 2-(trimethylsilyl)phenyl triflate with TBAF and an asymmetric vinyldihydropyridone. The resultant aryne Diels-Alder cycloadduct undergoes aromatization/eUmination to create the )V-acyl-/3-aminoketone (eq 13). This method was featured in a multistep synthesis of an unnatural a-amino acid. 

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