Unprecedented Synthesis of 3‑Alkenyl-3-ethoxy-2-iminoketones via 1,3-Dipolar Cycloadditions of Nitrones with Alkynyl Fischer Carbene Complexes

The synthesis of novel and highly substituted (2<i>Z</i>,3<i>Z</i>)-3-ethoxy-1-(aryl/cyclohexenyl)-4-aryl-2-(phenylimino)­but-3-en-1-one derivatives <b>24a</b>–<b>k</b> and <b>27a</b>–<b>e</b> by an unexpected and previously unreported [3 + 2] cycloaddition/rearrangement and ring-opening cascade process of the Fischer carbene complexes (CO)₅MC­(CC–Ar)­OCH₂CH₃ <b>1a</b>–<b>c</b> (M = Cr) and <b>1d</b>–<b>f</b> (M = W) and (CO)₅MC­(CC-cyclohexenyl)­OCH₂CH₃ <b>23a</b> (M = Cr) and <b>23b</b> (M = W) with <i>C</i>,<i>N</i>-diaryl nitrones (<b>7a</b>–<b>f</b>) is described. It is likely that the unstable 2,3-dihydroisoxazole carbene complexes produced in the [3 + 2] cycloaddition undergo a rapid and new rearrangement, followed by a stereoselective electrocyclic ring-opening process at a low temperature, to give only the (<i>Z</i>,<i>Z</i>) diastereoisomers <b>24a</b>–<b>k</b> and <b>27a</b>–<b>e</b> as the isolated products. The stereochemical assignment of the products was supported by NOE measurements and by single-crystal X-ray diffraction

Unprecedented Synthesis of 3‑Alkenyl-3-ethoxy-2-iminoketones via 1,3-Dipolar Cycloadditions of Nitrones with Alkynyl Fischer Carbene Complexes

The synthesis of novel and highly substituted (2<i>Z</i>,3<i>Z</i>)-3-ethoxy-1-(aryl/cyclohexenyl)-4-aryl-2-(phenylimino)­but-3-en-1-one derivatives <b>24a</b>–<b>k</b> and <b>27a</b>–<b>e</b> by an unexpected and previously unreported [3 + 2] cycloaddition/rearrangement and ring-opening cascade process of the Fischer carbene complexes (CO)₅MC­(CC–Ar)­OCH₂CH₃ <b>1a</b>–<b>c</b> (M = Cr) and <b>1d</b>–<b>f</b> (M = W) and (CO)₅MC­(CC-cyclohexenyl)­OCH₂CH₃ <b>23a</b> (M = Cr) and <b>23b</b> (M = W) with <i>C</i>,<i>N</i>-diaryl nitrones (<b>7a</b>–<b>f</b>) is described. It is likely that the unstable 2,3-dihydroisoxazole carbene complexes produced in the [3 + 2] cycloaddition undergo a rapid and new rearrangement, followed by a stereoselective electrocyclic ring-opening process at a low temperature, to give only the (<i>Z</i>,<i>Z</i>) diastereoisomers <b>24a</b>–<b>k</b> and <b>27a</b>–<b>e</b> as the isolated products. The stereochemical assignment of the products was supported by NOE measurements and by single-crystal X-ray diffraction

Unprecedented Synthesis of 3‑Alkenyl-3-ethoxy-2-iminoketones via 1,3-Dipolar Cycloadditions of Nitrones with Alkynyl Fischer Carbene Complexes

The synthesis of novel and highly substituted (2<i>Z</i>,3<i>Z</i>)-3-ethoxy-1-(aryl/cyclohexenyl)-4-aryl-2-(phenylimino)­but-3-en-1-one derivatives <b>24a</b>–<b>k</b> and <b>27a</b>–<b>e</b> by an unexpected and previously unreported [3 + 2] cycloaddition/rearrangement and ring-opening cascade process of the Fischer carbene complexes (CO)₅MC­(CC–Ar)­OCH₂CH₃ <b>1a</b>–<b>c</b> (M = Cr) and <b>1d</b>–<b>f</b> (M = W) and (CO)₅MC­(CC-cyclohexenyl)­OCH₂CH₃ <b>23a</b> (M = Cr) and <b>23b</b> (M = W) with <i>C</i>,<i>N</i>-diaryl nitrones (<b>7a</b>–<b>f</b>) is described. It is likely that the unstable 2,3-dihydroisoxazole carbene complexes produced in the [3 + 2] cycloaddition undergo a rapid and new rearrangement, followed by a stereoselective electrocyclic ring-opening process at a low temperature, to give only the (<i>Z</i>,<i>Z</i>) diastereoisomers <b>24a</b>–<b>k</b> and <b>27a</b>–<b>e</b> as the isolated products. The stereochemical assignment of the products was supported by NOE measurements and by single-crystal X-ray diffraction

Regioselective Synthesis of 1,2-Dihydroquinolines by a Solvent-Free MgBr₂‑Catalyzed Multicomponent Reaction

A highly efficient and regioselective synthesis of 1,2-dihydroquinolines via a multicomponent reaction between an aniline and two ketones is described. This reaction was catalyzed by magnesium bromide and carried out under solvent-free conditions. When the reaction was performed by using 3-substituted anilines and nonsymmetrically substituted ketones, principally a single product was found among the four expected regioisomers. A variety of anilines and ketones, including cyclic ketones, were evaluated providing a series of 1,2-dihydroquinolines with diverse substitution patterns. A study of the mechanism is discussed. There is evidence of the in situ formation of the imine as a result of the reaction between the aniline and one of the ketones, before annulation to the heterocyclic ring

Synthesis of <i>exo</i>-Imidazolidin-2-one Dienes, Their Isomerization, and Selectivity in Diels–Alder Cycloadditions

An efficient and alternative synthesis of <i>exo</i>-imidazolidin-2-one dienes is described. A condensation reaction was carried out with bis-imino derivatives, diacetyl, and triphosgene, affording symmetrically <i>N</i>,<i>N</i>-disubstituted dienes. The use of alkyl methyl α-diketones led to the formation of nonsymmetrical dienes, which underwent isomerization to provide more stable <i>inner-outer</i>-ring dienes under Lewis acid conditions. Evaluation was made of the reactivity as well as regio- and stereoselectivity of these dienes in Diels–Alder reactions. They proved to be highly reactive and selective. DFT calculations of the transition states accounted for their behavior

Divergent Pd-catalyzed Functionalization of 4‑Oxazolin-2-ones and 4‑Methylene-2-oxazolidinones and Synthesis of Heterocyclic-Fused Indoles

Palladium-catalyzed functionalization was presently performed on two building blocks: 4-oxazolin-2-ones and 4-methylene-2-oxazolidinones. Direct Heck arylation of 4-oxazolin-2-ones led to a series of 5-aryl-4-oxazolin-2-ones, including analogues with N-chiral auxiliary, in an almost quantitative yield. The Pd(II)-catalyzed homocoupling reaction of 4-oxazolin-2-ones provided novel heterocyclic across-ring dienes. Meanwhile, the intramolecular cross-coupling of N-aryl-4-methylene-2-oxazolidinones furnished a series of oxazolo[3,4-a]indol-3-ones. Further functionalization of 4-methylene-2-oxazolidinones afforded substituted indoles and heterocyclic-fused indoles with aryl, bromo, carbinol, formyl, and vinyl groups. A computational study was carried out to account for the behavior of the formylated derivatives. The currently developed methodology was applied to a new formal total synthesis of ellipticine

The Butterflies of Barro Colorado Island, Panama: Local Extinction since the 1930s

<div><p>Few data are available about the regional or local extinction of tropical butterfly species. When confirmed, local extinction was often due to the loss of host-plant species. We used published lists and recent monitoring programs to evaluate changes in butterfly composition on Barro Colorado Island (BCI, Panama) between an old (1923–1943) and a recent (1993–2013) period. Although 601 butterfly species have been recorded from BCI during the 1923–2013 period, we estimate that 390 species are currently breeding on the island, including 34 cryptic species, currently only known by their DNA Barcode Index Number. Twenty-three butterfly species that were considered abundant during the old period could not be collected during the recent period, despite a much higher sampling effort in recent times. We consider these species locally extinct from BCI and they conservatively represent 6% of the estimated local pool of resident species. Extinct species represent distant phylogenetic branches and several families. The butterfly traits most likely to influence the probability of extinction were host growth form, wing size and host specificity, independently of the phylogenetic relationships among butterfly species. On BCI, most likely candidates for extinction were small hesperiids feeding on herbs (35% of extinct species). However, contrary to our working hypothesis, extinction of these species on BCI cannot be attributed to loss of host plants. In most cases these host plants remain extant, but they probably subsist at lower or more fragmented densities. Coupled with low dispersal power, this reduced availability of host plants has probably caused the local extinction of some butterfly species. Many more bird than butterfly species have been lost from BCI recently, confirming that small preserves may be far more effective at conserving invertebrates than vertebrates and, therefore, should not necessarily be neglected from a conservation viewpoint.</p></div

Datasets used to compile a list of butterfly species collected or observed on BCI, 1923–2013.

<p>(*) Lycaenidae only. All records coded with year 1974, being the mid-point of 1962–1986, this period corresponding to the stay of G. Small in Panama.</p><p>(**) All records coded with year 2000, being the “mid-point” of 1996–2005.</p><p>The number of records (individuals) are indicated for the old and recent periods, as well as for the entire period of study.</p

The Butterflies of Barro Colorado Island, Panama: Local Extinction since the 1930s - Fig 1

<p>(a) Cumulative the number of individuals collected/observed plotted against the mean cumulative number of species collected/observed, for the recent period (1993–2013). Inset: cumulative no. of CTFS transects performed in the shady understory of BCI (2008–2013) plotted against the mean cumulative number of species collected/observed. Broken lines are 95% C.L. (b) Cumulative no. of individuals sequenced plotted against the cumulative no. of cryptic species discovered, for years 2008–2012. The grey line represents the best fit model, with its equation in inset.</p

Details of the % distribution of species richness within the 9 categories of abundance status

<p>(<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0136623#pone.0136623.t002" target="_blank">Table 2</a>) ordered by (a) faunal composition by families; (b) indices of host specificity; (c) host growth form; (d) indices of geographic distribution; (e) wing color pattern; and (f) wing size. For definition of (b), (d) and (e) indices, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0136623#pone.0136623.s011" target="_blank">S1 Text</a>.</p