Stereocontrolled synthesis of (3Z,5E)-6-aryl-3-methylhexa-3,5-dien-1-ols,intermediates in the synthesis of strobilurin antibiotics

(2E,4E)-5-Aryl-2-(2-benzyloxyethyl)penta-2,4-dien-1-als (aryl is phenyl and 4-methox-yphenyl) were reduced with NaBH₄ quantitatively and stereospecifically to the corresponding penta-2(E),4(E)-dien-1-ols. The hydroxymethyl group in the latter was transformed into a methyl one with a stereoselectivity of 92–97%. Debenzylation of the resulting (1E,3Z)-1-aryl-6-benzyloxy-4-methylhexa-1,3-dienes with AlCl₃ in the presence of PhNMe₂ afforded the target (3Z,5E)-6-aryl-3-methylhexa-3,5-dien-1-ols; the configuration of the C=C bonds in the conjugated aryl diene systems was retained at 95%.     

Formal synthesis of strobilurins A and X

Known synthetic precursors of strobilurins A and X, i.e., methyl (3Z,5E)-6-aryl-3-methylhexa-3,5-dienoates (aryl is phenyl, 4-methoxyphenyl), were synthesized by highly stereospecific reactions from 2-(2-tert-butyldimethylsilyloxyethyl)- and 2-[2-(4-methoxybenzyloxy)-ethyl]-5-arylpenta-2E,4E-dien-1-ols. These dienols were efficiently dehydroxylated to (1E,3Z)-4-methyl-6-(4-methoxybenzyloxy)hexa-1,3-dienylarenes with their subsequent demethoxyben-zylation to (3Z,5E)-6-aryl-3-methylhexa-3,5-dien-1-ols. The latter through the step of corresponding aryldienals and aryldienoic acids were transformed to the target methyl (3Z,5E)-6-aryl-3-methylhexa-3,5-dienoates, which completes a formal synthesis of strobilurins A and X. Configuration of the C=C bonds of the conjugated aryldiene system is preserved in the considered transformations by 95–97%.     

The total synthesis of strobilurin B

A new regio- and stereocontrolled total synthesis of the antibiotic strobilurin B is performed in nine steps in 5.5% overall yield.     

Structural component of disjoining pressure in wetting films of nitrobenzene formed on the lyophilic surface of quartz

It has been shown that a structural component of disjoining pressure, ν₈, decreasing according to the exponential law as the layer thickness increases, arises in the wetting films of nitrobenzene formed on the lyophilic surface of quartz. A family of isotherms, ν₈, have been obtained within a temperature range 293–333 K. The dependence of parameters on temperature has been determined, the parameters being characteristic of the transition of a wetting film into a thermodynamically nonequilibrium state.     

Highly stereoselective synthesis of 2,5-disubstituted (<Emphasis Type="Italic">E,E</Emphasis>)-penta-2,4-dienals

A condensation of α,β-unsaturated aldehydes with O-protected 4-hydroxybutanal N-(tert-butyl)-imine has been exemplified for the first time using (E)-cinnamic and (E)-4-methoxycinnamic aldehydes. (E,E)-2,5-Disubstituted penta-2,4-dienals, which are key intermediates in the synthesis of strobilurins A and X, were prepared in good yields and close to 100% stereoselectivity.     

Preparation of (2E,4E)-2-(2-benzyloxyethyl)-5-(3-methoxy-4-chlorophenyl)penta-2,4-dienal as a key intermediate in the synthesis of strobilurin B

(2E,4E)-2-(2-Benzyloxyethyl)-5-(4-chloro-3-methoxyphenyl)penta-2,4-dienal was obtained by the condensation of 4-benzyloxybutanal N-tert-butylimine with 4-chloro-3-methoxycinnamic aldehyde with ≥98% configurational purity and 40% yield. When 4-benzyloxy-2-triethylsilylbutanal imine was used, a 7: 3 mixture of the target (2E,4E)-dienal with its (2Z,4E)-isomer was obtained in 60% yield; the latter quantitatively isomerized to the thermodynamically preferable target (2E,4E)-dienal.     

Orientationally ordered layers of saturated hydrocarbons and their derivatives on quartz surfaces

The structure of the adjacent-to-wall layers of aliphatic hydrocarbons on quartz surface was investigated. Measurements of dichroism of the dyestuff molecules, or “guest” in the matrix of the basic substance, allowed establishing the presence of the orientational ordering in liquid layers at distances up to 200 nm. Additional measurements of the optical anisotropy (birefringence) in such layers have substantiated the existence of that ordering and its type. The structural characteristics of the adjacent-to-wall layers, such as thickness, type, and degree of the orientational ordering of molecules depend on the specific hydrocarbon used and the preparation (modification) of the surface of the solid substrate.