Dienic sex pheromones : Stereoselective syntheses of (7E,9Z)-7,9-dodecadien-1-yl acetate, (E)-9,11-dodecadien-1-yl acetate,and of (9Z), 11E)-9,11- tetradecadien-1-yl acetate by palladium-catalyzed reactions

Pure (7E,9Z-7, 9-dodecadien-1-yl acetate (1), the sex pheromone of Lobesiabotrana, has been prepared in 21.6% overall yield by a reaction scheme involving; (i) the cross-coupling of (E) - 8 - (2 - tetrahydropyranyloxy) -1 - octenyldisiamylborane with 1 - bromo - 1 - butyne, in the presence of a Pd (O) catalyst and base; (ii) the acetylation of the crude product of this reaction; (iii) the (Z)-stereoselective reduction of the obtained conjugated (E)-enyn-1-yl acetate. (E)-9,11-Dodecadien-1-yl acetate (2), a sex pheromone component of Diparopsiscastanea, has been analogously obtained (in 54.3% overall yield) by cross-coupling of (E) - 10 - (2 - tetrahydropyranyloxy) - 1 - decenyl borane with vinyl bromide, in the presence of a Pd (O) catalyst and base, followed by acetylation of the crude product. Compound 2, which was 87.7% chemically pure, was purified by column chromatography over SiO₂-AgNO₃. Chemically pure (9Z, 11E) - 9,11 - tetradecadien - 1 - yl acetate (3), a sex pheromone component of Spodopteralittoralis, has been prepared (in 30.2% overall yield) by reaction of 10 - (2 - tetrahydropyranyloxy) - 1 - decynylamagnesium bromide with (E)-1-iodo-1-butene, in the presence of a Pd (O) catalyst, followed by acetylation of the crude product and by (Z)-stereoselective reduction of the obtained (E)-enyn-1-yl acetate.The stereoisomeric purity of 1, 2 and 3 has been evaluated by glc analysis on glass capillary columns or by reverse phase hplc analysis.     

Asymmetric Synthesis of Highly Enantiomerically Enriched (S)(-)-β-Bisabolene

(S)-β-Bisabolene, (S)-1, was synthetized by a synthetic route in which (S)-4-methyl-3-cyclohexene carboxylic acid, (S)-10, which was the key intermediate, was prepared via a highly diastereoselective TiCl₄-catalyzed Diels-Alder reaction between isoprene and the acrylate of commercial (R)-pantolactone, followed by hydrolysis. Compound (S)-10 was then converted into ketone (S)-13 using two different procedures. The best one of these, as regards the degree of stereospecificity, involved the reaction of (S)-10 with 2 equiv of 4-methyl-3-penten-1-yllithium, 14, in the presence of CeCl₃, and gave (S)-13 having ca. 84% ee. The Zr-promoted methylenation of this ketone afforded highly enantiomerically enriched (S)-1.     

A TEMPO-catalyzed oxidation–reduction method to probe surface and anhydrous crystalline-core domains of cellulose microfibril bundles

Cellulose - A modified TEMPO-catalyzed oxidation of the solvent-exposed glucosyl units of cellulose to uronic acids, followed by carboxyl reduction with NaBD4 to 6-deutero- and...     

Synthesis and 13C nmr characterization of some π-excessive heteropolyaromatic compounds

Several π-excessive heteropolyaromatic compounds, which contain furan and thiophen ring and are possible antifungal agents, have been synthesized in good yields according to two general methods. The first method has been used to prepare compounds possessing thiophens linked by their 2- and 5-positions, such as the ter-aryls $\text{2b}$, $\text{2d}$ and $\text{2a}$. Two precursors of these compounds have been obtained either by the Glaser reaction, or using a novel Pd-mediated reaction. The second method,which consists of the Ni-or Pd-catalyzed heteroarylation of heteroarene halides via cross-coupling with heteroaryl Grignard reagents or zinc halides,has been used to prepare the bi-aryls $\text{1a-e}$, which contain two heteroaromatic units, and the ter-aryl $\text{2c}$. Compound $\text{1e}$ has been also prepared starting from 2-(2-thienyl) furan ($\text{1c}$) by selective lithiation, followed by bromination.The ¹³C NMR signals of $\text{1a-e}$ and $\text{2a-d}$ have been assigned on the basis of the literature data and by relaxation measurements. Relaxation data have been also used to obtain qualitative informations on the conformational equilibria of the bi-aryls $\text{1a}$, $\text{1c}$ and the ter-aryls $\text{2a-d}$.     

Synthesis of the two enantiomers of the sex pheromone of Diabrotica Undecimpunct at a Howardi and of chiral precursors of other pheromones starting from enantiomerically pure methyl hydrogen (R)-3-methylglutarate

Readily available methyl hydrogen (R)-3-methylglutarate(2) is a useful chiral building block for the synthesis of several biologically active compounds. Enantiomerically pure (R)-2 has been employed to synthesize stereospecifically each of the two enantiomers, 1a and 1b, of 10-methyl-2-tridecanone, the sex pheromone of the southern corn rootworm, Diabrotica undecimpunctata howardi Barber. Compound (R)-2 has been also used to prepare 99% optically pure (R)-3-methyl-1-pentanol (6) and enantiomerically pure (R)-5-methyl-i-tricosyne (7). These compounds are useful building blocks suitable for the further elaboration to other chiral insect pheromones.     

Synthetic Applications of Stereodefined 2-Substituted 1-Silyl-1-stannylethenes: A New Synthesis of 5-Ethenyl-5′-(1-propynyl)-2,2′-bithiophene,a Naturally-Occurring Phototoxin)

(E)-2-(5-Trimenthylstannyl-2-thienyl)ethenyldimethylphenylsilane. (E)-8, which can be stereospecifically prepared from (Z)-1-dimethylphenylsilyl-2-(2-thienyl)-1-trimethylstannyl-ethene, (Z)-6, or from (E)-2-(2-thienyl)ethenyldimethylphenylsilane, (E)-9, serves as an equivalent to the 2-ethenylthiophene d ¹', d ⁵-synthon, 20, in an efficient two-step synthesis of 5-ethenyl-5′-(1-propynyl)-2,2′-bithiophene, 10, a naturally-occurring phototoxin. In the first step of this synthesis compound (E)-8 undergoes a palladium-catalyzed cross-coupling reaction with 2-iodo-5-(1-propynyl)thiophene, 16, and in th second step the so obtained cross-coupling product, (E)-17, undergoes a protodesilylation reaction.     

Convenient copper- and solvent-free Sonogashira-type alkynylation of aryl iodides and bromides using Pd EnCat™

A straightforward methodology is described for the copper- and solvent-free alkynylations of aryl iodides and bromides using 0.1-0.01 mol % of Pd as Pd EnCat™ 40 or TPP30. High yielding reactions can be achieved under aerobic conditions for a variety of activated and deactivated aryl iodides; a few examples with aryl bromides are also described. Microwave irradiation is able to enhance yields and rates of these reactions.     

Insect sex pheromones: Palladium-catalyzed synthesis of aliphatic 1,3-enynes by reaction of 1-alkynes with alkenyl halides under phase transfer conditions

Functionalized 1,3-enzynes of general formula 1 have been prepared in good yields by coupling reaction of 1-alkynes or ω-functionalized 1-alkynes halides in the presence of a catalytic amount of (PPh₃)₄Pd and Cul. The reactions, which were carried out under phase transfer conditions employing benzyltriethylammonium chloride as phase transfer agent, benzene as organic solvent and diluted aq NaOH as base, occurred with 100% stereospecificity when 1-halo-1-alkenes of defined configuration were used. Such coupling reactions have been employed to prepare some pure insect sex pheromone components or their precursors in high overall yield.     

Naturally-occurring acetylenic compounds and derivatives : Regio- and stereocontrolled chloroformylation of 2-(1-propynyl)thiophene and 2-phenyl-5-(1-propynyl)thiophene

2-Phenyl-5-(1-propynyl)thiophene (1), isolated from Coreopsis grandiflora, and 2-(1-propynyl)thiophene (5), an immediate precursor in the synthesis of junipal (2), were synthesized in high yield by a Pd-catalyzed reaction between propyne and 2-iodo-5-phenylthiophene (4) or 2-iodothiophene (6), respectively. Reaction of 5 with the Vilsmeier reagent derived from POCl₃ and N-methylformanilide (MFA) afforded a mixture from which it was possible to isolate (E)-3-chloro-2-methyl-3-(2-thienyl)acrolein (10) in 37.7% yield. The structure and stereochemistry of 10 was unequivocally established by X-ray diffraction of a single crystal of the 2,4-dinitrophenylhydrazone of 10. GLC analysis showed that 10 was contaminated by ca 7% with an isomer to which, on the basis of ¹H-NMR and mass spectra, the structure of (Z)-3-chloro-2-methyl-3-(2-thienyl)acrolein (11) was attributed.Contrary to what was expected from the literature, junipal (2) represented only a minor component in the reaction mixture obtained by the Vilsmeier reaction on 5.Reaction of 1 with POCl₃ and MFA afforded (44.6% yield) a (E)-3-chloro-2-methylacrolein to which the structure 15 was attributed. Compound 15 was also contaminated by ca 10% of an isomer 16, which very probably corresponded to the (Z)-stereoisomer of 15.     

Candidate Trail Attractants of Reticultermes lucifugus: Stereoselective Syntheses of (3Z, 6E,BE)-(3Z, 6E, 8Z)-and (3Z, 6Z, 8Z)-3,6,8 -Dodecatrien-1-OL1

Stereoselective syntheses on a gram scale of (3Z,6E,8E)-, (3Z,6E,8Z)-and (3Z,6Z,8Z)-3,6,8-dodecatrien-1-ol, 8, 9 and 10, respectively, are described. A key step of the synthesis of 8 consisted of a copper-mediated coupling reaction between 4-(2-tetrahydropyranyloxy)-1-butynylmagnesium bromide (15) and the mesyl ester of (2E,4E)-2,4-octadien-1-ol (14). A similar copper-mediated reaction between 15 and the mesyl ester of (E)-2-octen-4-yn-1-ol (19) was used to construct the C-12 carbon skeleton of 9. On the other hand, the synthesis of 10 was based on a palladium-promoted reaction between (Z)-1-bromo-1-pentene (23) and the organozinc bromide derived from 3,6-heptadiyn-1-yl acetate (27).