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Known synthetic precursors of strobilurins A and X, i.e., methyl (3Z,5E) 6 aryl 3 methyl hexa 3,5 dienoates (aryl is phenyl, 4 methoxyphenyl), were synthesized by highly stereospe cific reactions from 2 (2 tert butyldimethylsilyloxyethyl) and 2 [2 (4 methoxybenzyloxy) ethyl] 5 arylpenta 2E,4E diеn 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 diеn 1 ols. The latter through the step of corre sponding 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 consid ered transformations by 95-97%.Strobilurins are biologically active compounds pro duced by bazidomicetes. 1 At present, there are known 15 representatives of this group of natural compounds of general formula 1 with different substituents in the ben zene ring. 2,3 The structures of some of them are given below.All the known strobilurins are capable of inhibiting the respiratory cycle in mitochondria and due to this exhibit high fungicide activity.The structure of strobilurins is characterized by the presence of a (E,Z,E) aryltriene fragment, whose stereo selective construction is poorly investigated. It is known from the literature that syntheses of strobilurins, except of one of them, 4 are based on the Wittig-Horner reaction and are not stereoselective.Retrosynthetic analysis of molecule 1 (Scheme 1) to gether with the method developed by us earlier 5 for the creation of internal (Z) trisubstituted C=C bond allowed us to expect success in development of highly stereoselec tive pathway for the construction of (3Z,5E) esters 2, the known 6,7 precursors of 1 and, thus, in accomplishment of formal total synthesis of compounds 1. 8 To check a plausibility of such an approach, for the synthesis of esters 2a (R 1 = R 2 = H) and 2b (R 1 = H, R 2 = OMe), precursors of simple strobilurins A (1A) and X (1X), earlier 9 we have accomplished the syntheses of (2E,4E) dienals 5a-c,e,f in high yields and stereoselec tivity ~100% (Scheme 2). The latter are the key interme diates in the approach under consideration, since they contain a required aryldiene fragment.The present work is aimed on the development of highly stereoselective methods for the transformation of dienals 5a-d through the steps of dienols 8a-d, dienols 3a,b, and dienoic acids 13a,b (see below) to esters 2a,b.Dienals 5a-d (see Scheme 2), like dienals 5e,f, 10 are smoothly and stereospecifically reduced with NaBH 4 un der standard conditions to give (2E,4E) dienols 8a-d. The structure of the latter was confirmed by elemental analysis and combination of physico chemical methods, first of all, NOE 1 H NMR. Thus, the olefinic region in the 1 H NMR spectrum of dienol 8a shows the presence of two doublets at δ 6.31 and 6.59, as well as a doublet of doublets at δ...

2E,4E) 5 Aryl 2 (2 benzyloxyethyl)penta 2,4 dien 1 als (aryl is phenyl and 4 methox yphenyl) were reduced with NaBH 4 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 AlCl 3 in the presence of PhNMe 2 afforded the target (3Z,5E) 6 aryl 3 methylhexa 3,5 dien 1 ols; the configuration of the C=C bonds in the con jugated aryl diene systems was retained at 95%.

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 syn thesis of strobilurins A and X, were prepared in good yields and close to 100% stereoselectivity.

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