V D Nageswara Sastri
Articles written in Proceedings – Section A
Volume 9 Issue 1 January 1939 pp 22-28
The action of mercuric acetate in methyl alcoholic solution on (1) umbelliferone, (2) 4-methylumbelliferone and (3) 4: 7-dimethylcoumarin has been investigated. With umbelliferone addition at the double bond and substitution in positions 6 and 8 take place whereas in the case of its 4-methyl derivative position 8 alone is mercurated to yield a monoacetoxymercuri-compound. In regard to the last compound the reaction stops with addition at the double bond and mercuration of the 6th position, the position 8 escaping the attack of the reagent. It is concluded that owing to the influence of the substitutent groups the reactivity of the three active centres of the coumarin molecule are differently affected.
Volume 10 Issue 4 October 1939 pp 267-274
The acetyl derivatives of coumaric, 4-methylcoumaric, 5-nitrocoumaric, psoralic and isopsoralic acids have been prepared and their behaviour studied under conditions which bring about
Volume 23 Issue 3 March 1946 pp 134-139
6∶7∶8-Trihydroxy and 6∶7∶8∶4′-tetrahydroxyflavones and their derivatives (methyl ethers and acetates) have been prepared starting with 2-hydroxy-3∶4∶5-trimethoxyacetophenone and adopting the Baker-Venkataraman procedure. Their properties and reactions have been studied and compared with those of the isomeric compounds, baicalein and scutellarein.
Volume 23 Issue 5 May 1946 pp 262-272
A simple and at the same time unambiguous method of synthesis of the 5∶6∶7-hydroxyflavones, baicalein and scutellarein and their derivatives is described. It starts from phloracetophenone which is partially methylated to the 4∶6-dimethyl ether. Oxidation of this ether with potassium persulphate yields the 2∶5-dihydroxy compound which on partial methylation produces 2-hydroxy-4∶5∶6-trimethoxyacetophenone. Using the benzoyl and anisoyl derivatives of this ketone and adopting the Baker-Venkataraman procedure, the trimethyl ether of baicalein and the tetramethyl ether of scutellarein have been prepared and from them the hydroxyflavones and their acetates.
Volume 23 Issue 5 May 1946 pp 273-277
Employing 2∶5-dihydroxy-4∶6-dimethoxyacetophenone and the Allan-Robinson method, the 5∶7-dimethyl ether of baicalein is obtained and from it by partial demethylation the 7-methyl ether. This is definitely different from oroxylin-A. The use of anisic anhydride in the above condensation yields two products, (1) 7∶4′-dimethyl ether of scutellarein and (2) 5∶7∶4′-trimethyl ether of 3-anisoyl-scutellarein. The former is different from the 6∶4′-dimethyl ether obtained from natural sources.
Volume 24 Issue 2 August 1946 pp 238-242
A satisfactory procedure for the preparation of 2-hydroxy-ω∶3∶6-trimethoxy-4-benzyloxy-acetophenone is described. Oxidation of this to the 2∶5-dihydroxyketone (IV), its condensation with the anhydride and sodium salt of benzoic acid and subsequent demethylation yield 6∶8-dihydroxygalangin. This constitutes a simplified method for the synthesis of 5∶6∶7∶8-hydroxyflavonols and their methyl ethers.
Volume 24 Issue 2 August 1946 pp 243-253
Since there was an element of uncertainty in the methods employed in the past for the synthesis of 5∶7∶8-hydroxyflavone derivatives, an unambiguous method has now been worked out. The required ketone, 2-hydroxy-3∶4∶6-trimethoxyacetophenone has been prepared by the partial methylation of 2∶4-dihydroxy-3∶6-dimethoxyacetophenone which is obtained directly from 1∶4-dimethoxy-2∶6-dibenzyloxybenzene by the Hoesch reaction. It has been converted into 5∶7∶8-trimethoxyflavone (wogonin-dimethyl ether) and 5∶7∶8∶4′-tetramethoxyflavone by the Baker-Venkataraman procedure. Even the above dihydroxyketone could be used for this purpose fairly satisfactorily and it yields as an intermediate stage 5∶8-dimethoxy-7-hydroxyflavone. Demethylation with hydrodic acid even under mild conditions is not satisfactory. Nor-wogonin is best obtained by employing anhydrous aluminium chloride in benzene solution for this reaction.
Volume 29 Issue 6 June 1949 pp 404-412
The method of demethylation using aluminium chloride in benzene medium is shown to be applicable to polymethoxy flavanones. 5∶7∶4′-, 5∶7∶8- and 5∶6∶7-trimethoxy flavanones yield the corresponding trihydroxy compounds. Similarly carthamidin and isocarthamidin are obtained from their tetramethyl ethers whose synthesis is described. This work provides synthetic confirmation of the constitution of these tetrahydroxy flavanones proposed by Kuroda. That no isomeric change takes place in the preparation of carthamidin is established by its methylation to its tetramethyl ether.
Volume 37 Issue 5 May 1953 pp 681-696