Chemistry of the Podocarpaceae. XLIX. Isomerization of 12-Methoxy-19-norpodocarpatetraenes

1974 ◽  
Vol 27 (9) ◽  
pp. 2017 ◽  
Author(s):  
RC Cambie ◽  
BA Grigor ◽  
RC Hayward ◽  
AJ Nielson
Keyword(s):  
Acid Chloride ◽  
Lead Tetraacetate ◽  
Oxidative Decarboxylation

Methods for isomerization of the 12-methoxy-19-norpodocarpatetraene mixture obtained from oxidative decarboxylation of 12-methoxypodocarpa-8,11,13-trien-19-oic acid (1) with lead tetraacetate have been examined. Acid-catalysed isomerization gives a mixture of the endocyclic isomers (11) and (19) while iodine-catalysed isomerization gives a mixture enriched in the isomer (19) to the extent of 80%. Metal-catalysed decarbonylation of the acid chloride (6) and oxidative decarboxylation of the acetoxy acid (7) have also been examined.

Oxidative decarboxylation of the 3-methyl-2-carboxynorbornanes with lead tetraacetate

1976 ◽  
Vol 54 (8) ◽  
pp. 1222-1225 ◽  
Author(s):  
J. B. Stothers ◽  
K. C. Teo
Keyword(s):  
Carboxylic Acids ◽  
Lead Tetraacetate ◽  
Starting Material ◽  
Oxidative Decarboxylation ◽  
Methyl Group

The mixtures of isomeric acetates produced by oxidative decarboxylation of the four 3-methyl-norbornane-2-carboxylic acids with lead tetraacetate in benzene have been characterized. The composition of these products depends primarily on the configuration of the methyl group in the starting material. The results are compared with those found for the Pb(OAc)4 decarboxylation of the norbornane-, bornane-, and 2,3,3-trimethylnorbornane-2-carboxylic acids. The formation of the products is interpreted in terms of competitive cationic and SNi substitution.

Selective cleavage of welan gum (S-130) by oxidative decarboxylation with lead tetraacetate

1996 ◽  
Vol 291 ◽  
pp. 109-114 ◽  
Author(s):  
N.Savitri Kumar ◽  
R.M. Sanjaya ◽  
K. Ratnayake ◽  
Göran Widmalm ◽  
Per-Erik Jansson
Keyword(s):  
Lead Tetraacetate ◽  
Oxidative Decarboxylation ◽  
Welan Gum

Synthesis of some bicyclo[2.2.2]oct-5-en-2-ones and bicyclo[2.2.2]octan-2-ones. Rearrangements accompanying oxidative decarboxylation with lead tetraacetate

1981 ◽  
Vol 59 (2) ◽  
pp. 344-355 ◽  
Author(s):  
Peter Yates ◽  
Gordon E. Langford
Keyword(s):  
Dicarboxylic Acid ◽  
Acyl Migration ◽  
Dicarboxylic Acids ◽  
Acid Group ◽  
Major Product ◽  
Lead Tetraacetate ◽  
Oxidative Decarboxylation ◽  
Similar Treatment ◽  
Carbonium Ion ◽  
A Minor

1-Methoxy-2-methyl-1,4-cyclohexadiene (3), 2-methoxy-1-methyl-1,3-cyclohexadiene (2), and 2-methoxy-1,5,5-trimethyl-1,3-cyclohexadiene (14) on heating with maleic anhydride give 1-methoxy-endo-7-methylbicyclo[2.2.2]oct-5-ene-syn-2,3-dicarboxylic acid anhydride (7) and its 6-methoxy-1-methyl (16a) and 6-methoxy-1,8,8-trimethyl (16b) analogues, respectively. On hydrolysis 16a and 16b give the corresponding keto dicarboxylic acids, 18a and 18b, via keto anhydrides 17a and 17b. Treatment of 18b with lead tetraacetate gives 1,8,8-trimethylbicyclo[2.2.2]oct-5-en-2-one (19) together with products in which rearrangement to a bicyclo[3.2.1]octane system has occurred. Treatment of 17b with bis(triphenylphosphino)nickel dicarbonyl gives only 19; similar treatment of 17a gives 1-methylbicyclo[2.2.2]oct-5-en-2-one (1). Reaction of bicyclo[2.2.2]octane-2,3-dione (27) with methyllithium gives 3-hydroxy-3-methylbicyclo[2.2.2]octan-2-one (28), its dimer 31, and a diol 30. Treatment of 5-exo-acetoxy-1, 5-endo-dimethyl-6-oxobicyclo[2.2.2]octane-anti-2,3-dicarboxylic acid (37) with lead tetraacetate gives 3-endo-acetoxy-1,3-exo-dimethyl-bicyclo[2.2.2]oct-5-en-2-one (33) as a minor product; the major product is derived by rearrangement to a bicyclo[3.2.1]octane system. It is proposed that this rearrangement, like that of 18b, involves oxidative decarboxylation of a single carboxylic acid group to give a carbonium ion that undergoes rearrangement via a 1,2-acyl migration.

The camphenehydro (methylcamphenilyl) and isobornyl (bornyl) cations. III. Oxidative decarboxylation of carboxylic acids with lead tetraacetate

1974 ◽  
Vol 27 (3) ◽  
pp. 603 ◽  
Author(s):  
GE Gream ◽  
CF Pincombe ◽  
D Wege
Keyword(s):  
Carboxylic Acid ◽  
Marked Change ◽  
Lead Tetraacetate ◽  
Dimethyl Sulphoxide ◽  
Oxidative Decarboxylation ◽  
Propanoic Acid ◽  
Acid Yield ◽  
Cupric Acetate ◽  
Initial Generation ◽  
Almost All

The oxidative decarboxylation of exo- and endo-bornane-2-carboxylic acid, exo- and endo-2,3,3- trimethylnorbornane-2-carboxylic acid and a-campholenylcarboxylic acid [3-(2',2',3'-trimethyl- cyclopent-3'-eny1)propanoic acid] with lead tetraacetate in benzene and dimethyl sulphoxide (each containing pyridine) in the presence, and absence, of cupric acetate has been investigated. The mode of formation of almost all the products can be satisfactorily rationalized in terms of the initial generation of radicals. In the case of exo- and endo-bornane-2-carboxylic acid, the derived bornyl radical forms organolead and organocopper derivatives that decompose in three ways: (1) by heterolysis by the direct route to give the equilibrating isobornyl and camphenehydro cations, (2) by a cyclic cis-elimination to give bornylene and (3) by an SNi process to give isobornyl and bornyl acetates. exo- and endo-2,3,3-Trimethylnorbornane-2-carboxylic acid yield the 2,3,3-trimethyl- norborn-2-yl radical which is converted into the equilibrating camphenehydro and isobornyl cations either by one-electron oxidation by lead species or via organolead or organocopper derivatives which undergo heterolysis. Processes involving cyclic cis-elimination and SNi substitution may also operate in the organometallic derivatives derived from the tertiary radical. a-Campholenylcarboxylic acid yields the a-campholenyl radical which, in the absence of cupric acetate, undergoes in the main cyclization to give the 2,3,3-trimethylnorbornyl radical. The resulting mixture of products is similar to that obtained from exo- and endo-2,3,3-trimethylnorbornane-2- carboxylic acid. In the presence of cupric acetate, the a-campholenyl radical is trapped at least to the extent of 50% in benzene and 80% in dimethyl sulphoxide to give the corresponding organo- copper derivative which undergoes a cyclic elimination to give 2,3,3-trimethyl-4-vinylcyclopentene and may undergo heterolysis by the x-route to give the camphenehydro and isobornyl cations. A marked change in the composition of the products on changing the solvent from benzene to dimethyl sulphoxide is observed only in the case of a-campholenylcarboxylic acid in the presence of cupric acetate.

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