Sintese total e estereosseletiva do (+-)-invictolideo. Componente do feromonio de reconhecimento da formiga Solenopsis invicta

AUTOR(ES)
DATA DE PUBLICAÇÃO

1991

RESUMO

Invictolide (1), a component of the queen recognition pheromone of Solenopsis invicta (imported fire ant) has been synthesized through three different routes, the relative stereochemistry at C(5), C(6) and C(1 ) being established using stereoselective aldols condensations (Scheme LXVIII). Route A required eight steps (24% overall yield) starting with the addition of the litihum enolate of BHT propanoate ( 48 ) to 2-methylvaleraldehyde (98% yield, 2:1 molar ratio of Felkin and anti-Felkin aldol 79a and 79b, respectively). After chromatographic separation the major diastereoisomer had its stereochemistry established by LAH carbonyl reduction, affording the know diol 83. Diol 83 was also a key intermediate in route B (ten steps, 13% overall yield) which employed the aldol condensation of sylilketenethioacetal 95 and aldehyde 97, promoted by an equivalent amount of TiCl4. The diastereoisomerically homogeneous aldol 98 (H- and C-RMN spectroscopies and GC analysis) had its relative stereochemistry established by homonuclear correlation espectroscopy (COSY) of the acetonides 101 and 104. Diol 100, obtained from the LAH reduction of 98, was monotosylated, chain elongated at C(1) with lithium diethylacuprate, followed by hydrogenolysis of the benzyl group to afford the key intermediate 83. The C-C bond formation through the intramolecular d-lactonization of tosylate 116 allowed the incorporation of the protecting group in the target structure affording a mixture of ()-invictolide 1 and ()-3-epi-invictolide 1 in 40:60 molar ratio, respectively, established by GC analysis. The desired stereochemistry at C(3) was accomplished through the following sequence: conversion of the above mixture to a 2:1 mixture of endo : exo insaturated lactones 130 and 131 (LDA/PhSeBr; H2O2/AcOH), chromatographic separation and hydrogenation (H2/Pd-C/EtOH) to afford ()-invictolide (1) as the major isomer (6:1 and 3:1 ratio, respectively). Route C (ten steps, 21% overall yield) employed aldol 98 which was converted to aldehyde 125 followed by Wittig-Horner homologation at C(5). Lactonization of the Z-a,b-unsaturated ester 127 and subsequent catalytic hydrogenation (H2/Pd-C/EtOH) afforded a 5:1 mixture of the desired product 129 and its C(3)-epimer 129 . Elongation of the side chain was achieved by tosylation followed by lithium diethylcuprate cross-coupling to afford ()-invictolide as the major isomer.

ASSUNTO(S)

quimica organica sintese organica

ACESSO AO ARTIGO

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