Acetyl substituted lactone

A versatile stereoselective synthesis of endo,exo-furofuranones was accomplished by R.C.D. Brown and coworkers. One of the key steps was a Rh(ll)-catalyzed C-H insertion reaction and the required diazo lactone was prepared via the Regitz diazo transfer reaction. The 2-acetyl substituted lactone substrate proved to be recalcitrant toward the deacylative diazo transfer under standard conditions. Eventually the authors decided to use the very reactive triflyl azide (TfNs), which was generated in situ under phase-transfer conditions to afford the desired a-diazo lactone. The C-H insertion product was then converted to (+)-methylxanthoxylol. 

These have a partial common structure, i.e. enolyzed a-diketone and a-hydrogen to the enollzable carbonyl is substituted by a methyl group. For a characteristic sugary aroma, the presence of enol-hydrogen was essential, because the acetyl ester or methyl ether of sotolon showed no characteristic aroma. The extraordinarily low threshold value of sotolon may be due to its coexistence with hydrophilic and hydrophobic (alkyl-substituted lactone) partial structures in one molecule. The lower threshold value of the ethyl-substituted homolog (II) than that of sotolon may also be explained from the balance of these opposite physicochemical properties. 

Benzo[c] cinnoline aldehydes are as yet unknown. The 2- and 3-acetyl derivatives have been prepared, but the majority of known compounds relevant to this section are mono- and dicarboxylic acid derivatives. These include the 2-, - - 3-, ° and 4. - o2.J55,i57 monoacids and esters, the lactone of 10-hydroxybenzo[c]cinnoline-l-carboxylic acid, some halogeno- and methyl-substituted 2- and 4. carboxylic acids, and the 2,9-, 3,8-, - - and 4,7- dicarboxylic acids and derivatives. These compounds have been obtained by ring synthesis, or, in the case of 2-methylbenzo[c]dnnoline-9-carboxylic acid, by side-chain oxidation, " rather than by the introduction of substituents into benzo[c] cinnoline. Benzo[c]cinnoline-l-carbonitrile has been prepared, albeit in low... 

The C-19 methyl group, in most cases, appears as a hydroxymethylene, either substituted with an acetyl group or formed an epoxy ring with different centers or could form a lactone. If the stereochemistry at C-5 is a, the substituents at C-19 would always be a. 

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