Identification and synthesis of macrolide pheromones of the grain beetle Oryzaephilus surinamensis and the frog Spinomantis aglavei.

Macrolide lactones, the so called cucujolides derived from unsaturated fatty acids, are aggregation pheromones of cucujid grain beetles. Thirty years ago, Oehlschlarger et al. showed that (3Z,6Z)-dodeca-3,6-dien-11-olide (4) and the respective 12-olide (7) attract the sawtoothed grain beetle Oryzaephilus surinamensis, whereas (5Z,8Z,13R)-tetradeca-5,8-dien-13-olide (5) increases the response synergistically. The frass of this beetle is attractive for its parasitoid Cephalonomia tarsalis, which potentially can be used for pest control. A GC/MS analysis of attractive frass showed the presence of 5, together with an unknown isomer. Cucujolide V was tentatively identified also in the femoral glands, pheromone-releasing structures, of the Madagascan mantelline frog Spinomantis aglavei. Therefore, a new route to synthesize doubly unsaturated macrolides allowing the flexible attachment of the side chain was developed. A straightforward method to obtain Z configured macrolides involves ring-closing alkyne metathesis (RCAM) followed by Lindlar-catalyzed hydrogenation. This methodology was extended to homoconjugated diene macrolides by using RCAM after introduction of one Z configured double bond in the precursor by Wittig reaction. A tungsten benzylidyne complex was used as the catalyst in the RCAM reaction, which afforded the products in high yield at room temperature. With the synthetic material at hand, the unknown isomer was identified as the new natural product (5Z,8Z,12R)-tetradeca-5,8-dien-12-olide, cucujolide X (8). Furthermore, the route also allowed the synthesis of cucujolide V in good yield. The natural products were identified by the synthesis of enantiomerically pure or enriched material and gas chromatography on chiral phases. The new macrolide (R)-8 proved to be biologically active, attracting female O. surinamensis, but no males. The synthetic material allowed the identification of (R)-5 in both the beetle and the frog.

Conjugated BODIPY DYEmers by metathesis reactions.

Boron dipyrrin (BODIPY) DYEmers bridged by conjugating ethynylene and ethenylene moieties can be prepared through metal-promoted metathesis reactions. Alkyne metathesis was advantageous over alkene metathesis and Stille coupling for BODIPY substrates, but also showed specific restrictions with respect to steric encumbrance and regioselectivity. All derivatives with unhindered rotations along the bridges reside in a coplanar minimum conformation. For a hindered ß-ethenylene-bridged DYEmer, the shifts in the (1) H NMR spectrum indicate a significant loss of coplanarity and conjugation. The electronic interactions of the BODIPY subchromophores, visualized by optical spectra and cyclic voltammograms, deviate significantly from those found for nonconjugated and excitonically coupled DYEmers. The observed properties can be rationalized in each case by the respective strength of conjugation through the α or ß position, the degree of coplanarity, and conformational dynamics.

Efficient metathesis of terminal alkynes.

Now even terminal: The 2,4,6-trimethylbenzylidyne complexes [MesC≡M{OC(CF(3))(2)Me}(3)] (M=Mo, W) were synthesized from [Mo(CO)(6)] and [W(CO)(6)], respectively. The molybdenum complex is an efficient catalyst for the metathesis of internal and terminal alkynes and also for the ring-closing metathesis of internal and terminal α,ω-diynes at room temperature and low catalyst concentrations.

Preparation of imidazolin-2-iminato molybdenum and tungsten benzylidyne complexes: a new pathway to highly active alkyne metathesis catalysts.

The reaction of [PhC[triple bond]MBr(3)(dme)] (dme=1,2-dimethoxyethane) with the hexafluoro-tert-butoxides LiX or KX [X=OC(CF(3))(2)Me] afforded the benzylidyne complexes [PhC[triple bond]MX(3)(dme)] (2a: M=W, 2b: M=Mo), which further reacted with the lithium reagent Li(Im(tBu)N), generated with MeLi from 1,3-di-tert-butylimidazolin-2-imine (Im(tBu)NH), to form the imidazolin-2-iminato complexes [PhC[triple bond]MX(2)(Im(tBu)N)] (3a: M=W, 3b: M=Mo). The propylidyne complex [EtC[triple bond]MoX(2)(NIm(tBu))] (4) was obtained by treatment of 3b with an excess of 3-hexyne. Complexes 3a and 3b are able to efficiently catalyse alkyne cross metathesis of various 3-pentynyl benzyl ethers 5 and benzoic esters 7 at room temperature, to afford 2-butyne and the corresponding diethers 6 and diesters 8. The tungsten complex 3a proved to be a superior catalyst for ring-closing alkyne metathesis, and the [10]cyclophanes 10 and 12 were synthesised in high yield from 1,3-bis(3-pentynyloxymethyl)benzene (9) and bis(3-pentynyl) phthalate (11), respectively. The molecular structures of compounds 2a, 2b, 3a, 3b, 4, and 12 were determined by single-crystal X-ray diffraction. DFT calculations have been carried out for catalyst systems based on the imidazolin-2-iminato tungsten and molybdenum complexes 3a and 3b by choosing the alkyne metathesis of 2-butyne as the model reaction; the studies revealed a lower activation barrier for the tungsten system.