Formation of a two-dimensional periodic structure of local melting regions on a silicon surface upon pulsed light irradiation

The first results regarding the formation of a two-dimensional periodic structure of local melting regions on a silicon surface upon pulsed light irradiation are presented. The conditions are established, and the mechanism of the formation of such structures is discussed. Zh. Tekh. Fiz. 67, 97–99 (December 1997)     

Orifluoroacetylation and dehydration of 20-hydroxyecdysone acetonides. Synthesis of stachisterone B

Orifluoroacetylation of the 25(OH)-group with subsequent dehydration of the 14(OH)-group takes place in the reaction of 20-hydroxyecdysone 20,22-acetonide and 2,3:20,22-diacetonide with trifluoroacetic anhydride in the presence of pyridine. Dehydration of the 14(OH)-group gives rise to stachisterone B derivatives, which are hydrolyzed to give the phytoecdysteroid stachisterone B.     

7α-alkylation, 7,7-bisalkylation,and reduction of the 20-oxo group of poststerone in reactions with alkyl halides in lithium–ammonia solution

Reactions of poststerone with methyl iodide, allyl bromide, and propargyl bromide in lithium–ammonia solution resulted in its completely stereoselective 7α-alkylation accompanied by reduction of the 20-oxo group with formation of equimolar amounts of 20R- and 20S-hydroxy derivatives. The reaction of poststerone with excess allyl bromide afforded 7,7-bis-allyl 20R- and 20S-alcohols at a ratio of 3: 1. The reduction of the 20-oxo group in the alkylation of poststerone with excess propargyl bromide led to the formation of an equimolar mixture of Δ⁸⁽¹⁴⁾- and Δ⁸⁽⁹⁾-isomers with exclusive S configuration of C²⁰.     

Synthesis of Phosphorylated Derivatives of Enamino-Carbonyl Compounds

Abstract

The reactions of enaminocarbonyl compounds (1) with phosphorylisocyanates have been investigated. Experiment established that the reactions with the participation of amino group and (or) C-2 atom form respectively ureas (2) and (or) their vinylogs (3) depending on the structure (1) i.e. the reactions proceed in two competitive directions.     

One class of equations solvable in radicals

We derive recurrent formulas for obtaining minimal polynomials for values of tangents and show that Galois groups of these polynomials are commutative. Thus we give examples of equations of arbitrarily high degrees solvable in radicals.     

9α-hydroxylation of 25-fluoroponasterone a diacetonide in lithium-ammonia solution

25-Fluoroponasterone A diacetonide reacted with lithium in liquid ammonia to give 25-fluoro-9α,20-dihydroxyecdysone diacetonide whose hydrolysis afforded 25-fluoro-9α,20-dihydroxyecdysone 20,22-acetonide. Nonfluorinated analog of the latter was isolated previously from Silene italica ssp. nemoralis.     

Method for mild trimethylsilylation of the 14α-hydroxy group in ecdysteroids

In the reactions of poststerone derivatives and 20-hydroxyecdysone with (trifluoromethyl)trimethylsilane catalyzed by tetrabutylammonium fluoride, the 14-hydroxy group is readily subjected to trimethylsilylation.     

Δ<Superscript>8(14)</Superscript>-14α-deoxy- and 14α-deoxy-14α-hydroperoxyecdysteroids

Δ⁸⁽¹⁴⁾-14α-deoxy- and 14α-deoxy-14α-hydroperoxyecdysteroids were synthesized, the reduction of Δ⁸⁽¹⁴⁾-14α-deoxy-20-hydroxyecdysone diacetonide at treatment with complex hydrides of alkali metals was investigated, and the stereochemistry of the obtained 6-hydroxy derivative and its acetate was established.