ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
It is shown that the 2-(hydroxymethyl)-1-methylazulenes 6 are being oxidized by activated MnO2 in CH2Cl2 at room temperature to the corresponding azulene-1,2-dicarbaldehydes 7 (Scheme 2). Extension of the MnO2 oxidation reaction to 1-methyl- and/or 3-methyl-substituted azulenes led to the formation of the corresponding azulene-1-carbaldehydes in excellent yields (Scheme 3). The reaction of unsymmetrically substituted 1,3-dimethyl-azulenes (cf. 15 in Scheme 4) with MnO2 shows only little chemoselectivity. However, the observed ratio of the formed constitutionally isometric azulene-1-carbaldehydes is in agreement with the size of the orbital coefficients in the HOMO of the azulenes. The reaction of guaiazulene (18) with MnO2 in dioxane/H2O at room temperature gave mainly the expected carbaldehyde 19. However, it was accompanied by the azulene-diones 20 and 21 (Scheme 5). The precursor of the demethylated compound 20 is the carbaldehyde 19. Similarly, the MnO2 reaction of 7-isopropyl-4-methyalazulene (22) as well as of 4,6,8-trimethylazulene (24) led to the formation of a mixture of the corresponding azulene-1,5-diones and azulene-1,7-diones 20/23 and 25/26, respectively, in decent yields (Schemes 6 and 7). No MnO2 reaction was observed with 5,7-dimethylazulene.
Additional Material:
2 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19950780603
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