Total Synthesis of (+)-Antrocin and Its Diastereomer and Clarification of the Absolute Stereochemistry of (-)-Antrocin.

Using 2,2-dimethyl cyclohexanone as the starting compound, (+)-antrocin and its diastereomer have been synthesized. The absolute stereochemistry of (-)-antrocin, a natural sesqui-terpenoid and an antagonist in some types of cancer cells, was clarified using the character data of (+)-antrocin. The synthetic procedure involved two key steps: (1) the reaction of vinyl magnesium bromide with 2,2-dimethyl-6-t-butyl-dimethyl-silyoxy-methyl-1-cyclo-hexanone to give a vinyl cyclohexanol derivative and (2) a highly stereoselective intramolecular Diels-Alder (IMDA) reaction of the camphanate-containing triene intermediate. The relative energy levels of the possible transition states of the IMDA reaction of the camphanate-containing triene were obtained from density functional theory calculations, proving the stereospecific formation of the target molecule.

The effect of substituents on triply bonded boron[triple bond, length as m-dash]antimony molecules: a theoretical approach.

Three (M06-2X/Def2-TZVP, B3PW91/Def2-TZVP and B3LYP/LANL2DZ+dp) levels of theory are used to study the effect of substituents on the potential energy surfaces of RB[triple bond, length as m-dash]SbR (R = F, OH, H, CH3, SiH3, SiMe(SitBu3)2, SiiPrDis2 and NHC). The theoretical results demonstrate that the triply bonded RB[triple bond, length as m-dash]SbR molecules favor a bent geometry: that is, ∠R-B-Sb ≈ 180° and ∠B-Sb-R ≈ 120°. Regardless of the type of substituents that are attached to the RB[triple bond, length as m-dash]SbR compounds, theoretical evidence strongly indicates that their B[triple bond, length as m-dash]Sb triple bonds have a donor-acceptor nature and are proven to be very weak. Two valence bond models clarify the bonding characters of the B[triple bond, length as m-dash]Sb triple bond. For RB[triple bond, length as m-dash]SbR molecules that feature small substituents, the triple bond is represented as . For RB[triple bond, length as m-dash]SbR molecules that feature large substituents, the triple bond is represented as . Most importantly, this theoretical study predicts that only bulkier substituents significantly stabilize the triply bonded RB[triple bond, length as m-dash]SbR molecules, from the kinetic viewpoint.

Triply Bonded Gallium≡Phosphorus Molecules: Theoretical Designs and Characterization.

The effect of substitution on the potential energy surfaces of triple-bonded RGa≡PR (R = F, OH, H, CH3, SiH3, SiMe(SitBu3)2, SiiPrDis2, Tbt (C6H2-2,4,6-{CH(SiMe3)2}3), and Ar* (C6H3-2,6-(C6H2-2,4,6-i-Pr3)2)) compounds was theoretically examined by using density functional theory (i.e., M06-2X/Def2-TZVP, B3PW91/Def2-TZVP, and B3LYP/LANL2DZ+dp). The theoretical evidence strongly suggests that all of the triple-bonded RGa≡PR species prefer to select a bent form with an angle (∠Ga-P-R) of about 90°. Moreover, the theoretical observations indicate that only the bulkier substituents, in particular, for the strong donating groups (e.g., SiMe(SitBu3)2 and SiiPrDis2) can efficiently stabilize the Ga≡P triple bond. In addition, the bonding analyses (based on the natural bond orbital, the natural resonance theory, and the charge decomposition analysis) reveal that the bonding characters of such triple-bonded RGa≡PR molecules should be regarded as [Formula: see text]. In other words, the Ga≡P triple bond involves one traditional σ bond, one traditional π bond, and one donor-acceptor π bond. Accordingly, the theoretical conclusions strongly suggest that the Ga≡P triple bond in such acetylene analogues (RGa≡PR) should be very weak.

Substituent Effects on the Stability of Thallium and Phosphorus Triple Bonds: A Density Functional Study.

Three computational methods (M06-2X/Def2-TZVP, B3PW91/Def2-TZVP and B3LYP/LANL2DZ+dp) were used to study the effect of substitution on the potential energy surfaces of RTl≡PR (R = F, OH, H, CH3, SiH3, SiMe(SitBu3)2, SiiPrDis2, Tbt (=C6H2-2,4,6-(CH(SiMe3)2)3), and Ar* (=C6H3-2,6-(C6H2-2, 4,6-i-Pr3)2)). The theoretical results show that these triply bonded RTl≡PR compounds have a preference for a bent geometry (i.e., ∠R⎼Tl⎼P ≈ 180° and ∠Tl⎼P⎼R ≈ 120°). Two valence bond models are used to interpret the bonding character of the Tl≡P triple bond. One is model [I], which is best described as TlP. This interprets the bonding conditions for RTl≡PR molecules that feature small ligands. The other is model [II], which is best represented as TlP. This explains the bonding character of RTl≡PR molecules that feature large substituents. Irrespective of the types of substituents used for the RTl≡PR species, the theoretical investigations (based on the natural bond orbital, the natural resonance theory, and the charge decomposition analysis) demonstrate that their Tl≡P triple bonds are very weak. However, the theoretical results predict that only bulkier substituents greatly stabilize the triply bonded RTl≡PR species, from the kinetic viewpoint.

Large Submillimeter Assembly of Microparticles with Necklace-like Patterns Formed by Laser Trapping at Solution Surface.

In colloidal solution, nanoparticles can be optically trapped by a tightly focused laser beam, and they are assembled in a focal spot whose diameter is typically about one micrometer. We herein report that a large submillimeter sized assembly of polystyrene microparticles with necklace-like patterns are prepared by laser trapping at a solution surface. The light propagation outside the focal spot is directly confirmed by 1064 nm backscattering images, and finite difference time domain simulation well supports the idea that an optical potential is expanded outside the focal spot based on light propagation through whispering gallery mode. This demonstration opens a new method for fabrication of a millimeter-order huge assembly by a single tightly focused laser beam.

Triple-Bonded Boron≡Phosphorus Molecule: Is That Possible?

The effect of substitution on the potential energy surfaces of RB≡PR (R = H, F, OH, SiH3, and CH3) is studied using density functional theories (M06-2X/Def2-TZVP, B3PW91/Def2-TZVP, and B3LYP/LANL2DZ+dp). There is significant theoretical evidence that RB≡PR compounds with smaller substituents are fleeting intermediates, so they would be difficult to be detected experimentally. These theoretical studies using the M06-2X/Def2-TZVP method demonstrate that only the triply bonded R'B≡PR' molecules bearing sterically bulky groups (R' = Tbt (=C6H2-2,4,6-{CH(SiMe3)2}3), SiMe(SitBu3)2, Ar* (=C6H3-2,6-(C6H2-2,4,6-i-Pr3)2), and SiiPrDis2) are significantly stabilized and can be isolated experimentally. Using the simple valence-electron bonding model and some sophisticated theories, the bonding character of R'B≡PR' should be viewed as R'BI PR'. The present theoretical observations indicate that both the electronic and the steric effect of bulkier substituent ligands play a key role in making triply bonded R'B≡PR' species synthetically accessible and isolable in a stable form.

Is It Possible To Prepare and Stabilize Triple-Bonded Thallium≡Antimony Molecules Using Substituents?

The M06-2X/Def2-TZVP, B3PW91/Def2-TZVP, and B3LYP/LANL2DZ+dp levels of theory were used to investigate the effect of substituents on the stability of the triple-bonded RTl≡SbR molecule. For comparison, small groups (F, OH, H, CH3, and SiH3) and sterically bulky substituents, (Ar* (=C6H3-2,6-(C6H2-2,4,6-i-Pr3)2), Tbt (=C6H2-2,4,6-{CH(SiMe3)2}3), SiiPrDis2, and SiMe(SitBu3)2), were chosen for the present study. The density functional theory results indicate that the triple-bonded RTl≡SbR compounds with small ligands are transient intermediates, so their experimental detections should be extremely difficult. Nevertheless, the theoretical observations demonstrate that only the bulkier ligands can effectively stabilize the central Tl≡Sb triple bond. In addition, the valence-electron bonding model reveals that the bonding characters of the triple-bonded RTl≡SbR species possessing sterically bulky groups can be represented as RTl ← SbR. Nevertheless, on the basis of the natural resonance theory, the natural bond orbital, and the charge decomposition analysis, the theoretical observations suggest that the Tl≡Sb triple bond in the acetylene analogues, RTl≡SbR, should be very weak.

Indium-Arsenic Molecules with an In≡As Triple Bond: A Theoretical Approach.

The effect of substitution on the potential energy surfaces of RIn≡AsR (R = F, OH, H, CH3, and SiH3 and R' = SiMe(SitBu3)2, SiiPrDis2, and N-heterocyclic carbene (NHC)) is determined using density functional theory calculations (M06-2X/Def2-TZVP, B3PW91/Def2-TZVP, and B3LYP/LANL2DZ+dp). The computational studies demonstrate that all of the triply bonded RIn≡AsR species prefer to adopt a bent geometry, which is consistent with the valence electron model. The theoretical studies show that RIn≡AsR molecules that have smaller substituents are kinetically unstable with respect to their intramolecular rearrangements. However, triply bonded R'In≡AsR' species that have bulkier substituents (R' = SiMe(SitBu3)2, SiiPrDis2, and NHC) occupy minima on the singlet potential energy surface, and they are both kinetically and thermodynamically stable. That is, the electronic and steric effects of bulky substituents play an important role in making molecules that feature an In≡As triple bond viable as a synthetic target. Moreover, two valence bond models are used to interpret the bonding character of the In≡As triple bond. One is model [A], which is best represented as . This interprets the bonding conditions for RIn≡AsR molecules that feature small ligands. The other is model [B], which is best represented as . This explains the bonding character of RIn≡PAsR molecules that feature large substituents.

The effect of substituents on the stability of triply bonded gallium[triple bond, length as m-dash]antimony molecules: a new target for synthesis.

The effect of substitution on the potential energy surfaces of RGa-[triple bond, length as m-dash]Sb+R (R = F, OH, H, CH3, SiH3, SiMe(SitBu3)2, SiiPrDis2 and NHC) is studied using density functional theory (M06-2X/Def2-TZVP, B3PW91/Def2-TZVP and B3LYP/LANL2DZ + dp). The computational results show that all of the triply bonded RGa-[triple bond, length as m-dash]Sb+R molecules have a preference for a bent geometry (i.e., ∠RGaSb ≈ 180° and ∠GaSbR ≈ 90°), which can be described using a valence bond model. The theoretical results show that because RGa-[triple bond, length as m-dash]Sb+R has smaller electropositive groups, it could be both kinetically and thermodynamically stable and may be experimentally detectable. However, these theoretical results predict that the triply bonded R'Ga-[triple bond, length as m-dash]Sb+R' molecules that have bulkier groups (R' = SiMe(SitBu3)2, SiiPrDis2, and NHC) are kinetically stable. In other words, both the electronic and the steric effects of bulkier substituent groups mean that it should be possible to experimentally isolate triply bonded RGa-[triple bond, length as m-dash]Sb+R molecules in a stable form.