Ketones from acetoxy epoxides

The oxidation of manool has been re-examined with the aim of producing ambergris-type perfumes. Oxidation with potassium permanganate afforded the known s methyl ketone (6), the diether (7), and at 40 °C the lactone (8). Sodium dichromate gave the aldehyde (9) as a mixture of E- and Z-isomers. Further oxidation of the methyl ketone with hypobromite gave an a-hydroxy-acid (10) and an ether (11) which was also obtained from manoyl oxide. Oxidation of the ketone with per-acid gave an acetoxy-epoxide which on reduction with lithium aluminium hydride afforded a diol. This was converted into an odoriferous ether (12). The ready formation of 5- and 6-membered-ring ethers of this type is a characteristic feature of this area of diterpenoid chemistry. 

An a-acetoxy-epoxide is readily prepared from the corresponding ketone by peracid treatment of the enol acetate. The acetoxy-epoxide reacts with a cuprate reagent in the manner shown in Scheme 37, resulting in overall a-alkylation of the ketone. Unfortunately, the product yield varies widely, depending on the nature of the organocuprate reagent and the structure of the acetoxy-epoxide. ... 

While enol acetates from saturated ketones were useful a-oxygenation substrates, the corresponding dienol acetates are not. The relatively electron-deficient alkene bearing the acetoxy group is less attractive h> elecm hilic oxygenating agents than the unsubstituted double bond. Thus, for example, peracid treatment leads to epoxidation the unfiinctionalized alkene.However, it would seem likely that re-... 

A la-acetoxy-derivative of ozic acid (5) and the 12,13-epoxide (6) were amongst the diterpenoids obtained" from Mikania (Compositae) species. The angelate and tiglate esters of 19-hydroxylabd-7,13-dien-15-oic acid were isolated" from Brickellia argyrolepsis (Compositae). The corresponding diol, villenol, the 7a-alcohol, villenatriol, the 7-ketone, villenolone, and the 7-keto-... 

Hydrogen bromide-catalysed rearrangement of lupenyl acetate affords the olefin (104) which is readily isomerized to (105). Epoxidation of the latter gave the a-epoxide (106), whose structure was confirmed by X-ray analysis. Hydro-boronation of 3/3-acetoxy-30-norlup-19-ene (107) results in addition from the a-face with formation of the 19aH-alcohol (lOS). " The corresponding ketone (109), which undergoes facile epimerization at C-19 in base, was converted into 19aH-lupeol (110), whose spectroscopic properties cast doubt on the recent... 

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