Alicyclic ketones, rearrangement

Formation of lactams 431 was achieved in good yields (60-86%) by allowing a mixture of alicyclic-ketones 429 and hydroxylamine-(9-sulfonic acid adsorbed on Si02 to be irradiated in a focused MW oven for 10-20 min (Scheme 85). The reaction proceeded by forming the oxime 430 and sulfuric acid, which promoted a Beckmann rearrangement of 430 to give lactams 431 (95JCS(CC)1101). 

Reduction of enol ethers or enol esters of 1,3-diketones, followed by acid-catalyzed allylic rearrangement of the reduction product (see p. 85 in ref. 5) is a useful route to a,P-unsaturated ketones. Ali-phatic - and alicyclic enones have thus been prepared in good yields at low temperatures with NaAlH2(0CH2CH20Me)2.2 6... 

Rearrangements to unsaturated ketones with hydrogen or alkyl migration have been observed in the acetone-sensitized reactions of cyclic and alicyclic 3,4-epoxy-olefins (Eq. 331). ° ... 

The ring contraction rearrangement of alicyclic a-diketones is much more valuable from the synthetic viewpoint e.g. equation 4). There are several routes available for the synthesis of a-diketones from monoketones. These include direct oxidation using selenium dioxide permanganate or osmium tetrox-ide addition across the double bond of an enone followed by base-promoted elimination of water bromi-nation to give the dibromo ketone followed by hydrolysis condensation with 4-nitroso-/V,/V-dimethylaniline followed by acidic hydrolysis — but there are many others. The bromination-hydrolysis route has been extensively studied by Wallach." The conversion of menthone into 1-hydroxy-... 

Ketocarbenes of type (21) obtained from acyclic and medium to large ring alicyclic a-diazo ketones (20) are prone to react by way of an intramolecular [1,2] H-shift, especially under catalytic conditions, to afford a, 3-unsaturated ketones (22). °4 -60 Pranzen has shown that the Wolff rearrangement of diazo ketones (20) is favored if temperatures in excess of 100 °C are used in the photochemical or Ag20-pro-moted decompositions. Related [1,2] methyl shifts can also occur, and this pathway is the principal decomposition route of 4-diazo-2,2,5,5-tetramethyl-3-hexanone. ... 

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