Padmakar L. Joshi

Facile synthesis of meso-substituted dipyrromethanes and porphyrins using cation exchange resins

The macroporosity and acidity of cation exchange resins play a crucial role in the synthesis of dipyrromethanes and porphyrins; for the first time, cation exchange resins have been used as heterogeneous solid acid catalysts to produce dipyrromethanes and porphyrins in good yields. The reaction, at room temperature, of substituted aromatic aldehydes with pyrrole catalysed by cation exchange resin afforded the corresponding meso-substituted dipyrromethane in yields ranging from 70 to 80%, indicating the broad scope of the reaction. Further, the condensation of meso-substituted dipyrromethane with similar or different substituted aromatic aldehydes, using cation exchange resins furnished meso-tetrakis-symmetrical and mixed porphyrins, respectively. One-pot synthesis of porphyrins can also be carried out directly from the aldehydes and pyrrole under the above conditions. Acidolysis of the dipyrromethane is negligible under the conditions of the porphyrin-forming reaction.

Stereoselective synthesis of (22R, 23R, 24S)-3β-hydroxy-5-ene-22, 23-dihydroxy-24-methyl-cholestane : a brassinolide intermediate from 16-dehydropregnenolone acetate

Abstract A new synthesis of the important aldehyde 1 from easily available 16-Dehydropregnenolone acetate (16-DPA) in high yield is described. The aldehyde 1 is converted to trio] 24, involving a stereoselective generation of all the four chiral centers in the brassinolide side chain. The important features of this synthesis is stereospecific generation of the acetate 14 through ene reaction using three different catalysts as well as regioselective wittig reaction on the acetoxy aldehyde 20. Conversion of triol 24 to brassinolide is known, hence this constitutes a formal total synthesis of brassinolide.

Resin catalysed ene reaction on 3β-toluene-p-sulfonoxy-(Z)-pregna-5,17(20)-diene : synthesis of (20S)-6β-methoxy-3α,5-cyclo-5α-pregnane-20-carboxyaldehyde+

Abstract Conversion of 17-keto steroid 2 in to 17(Z) ethylidene steroid 3 was achieved in high yields using a modified procedure. Ene reaction on 4 with paraformaldehyde in presence of acetic anhydride using various cation exchange resins as catalyst afforded stereospecifically the C-22 acetate 5 in excellent yields. For the first time cation exchange resins have been used as catalysts in ene reaction. Compound 5 was converted to C-22 aldehyde 1 using simple reaction sequence.

Synthesis of 11β-(4-dimethylaminophenyl)-17β-hydroxy-17α- (3-methyl-1-butynyl)-4, 9-estradien-3-one and 11β-(4-acetophenyl)- 17β-hydroxy-17α-(3-methyl-1-butynyl)-4, 9-estradien-3-one: two new analogs of mifepristone (RU-486)☆,☆☆,☆☆☆

From the structure activity relationship, two new analogs, 2 and 3, of the potent progesterone antagonist mifepristone 1 have been designed. The syntheses of these two analogs have been achieved in eleven steps through modified synthetic sequences and improved procedures starting from (+)-estrone. In comparison with mifepristone 1, the relative binding affinities of compound 2 for the progesterone receptor was found to be more, whereas that of compound 3 was less.

Short-step stereoselective synthesis of 2α,3α,22-triacetoxy-23,24-dinor-5α-cholan-6-one: key intermediate for the preparation of 24-norbrassinolide, dolicholide and dolichosterone

A stereoselective synthesis of 6-oxo-23,24-dinor-5α-cholan-2α,3α,22-triyl triacetate 9 was achieved in 44% overall yield in nine steps starting from 3β-hydroxyandrost-5-en-17-one 8. The important features of this synthesis are the modified Wittig reaction on the 17-oxo steroid 8 and the stereospecific generation of the chiral centre at C-20 by a resin-catalysed ene reaction on (Z)-3β, p-tolylsulfonyloxypregna-5,17(20)-diene 11.

Influence of an Oxidising Impurity on Preparation of 2-Lithio-1,3-dithiane: Isolation of bis[2-d,3-Dithianyl)]methanol

Abstract Bis-dithianylalkanols and dimers are formed in preparation of 2-lithio-1,3-dithianes due to the presence of oxidising impurity in n-BuLi (perhaps n-BuOOLi).