A practical synthesis of (−)-kazusamycin A (revised)

We describe herein a stereo-controlled and practical synthesis of three key building blocks, namely Segment AB′, Segment D, and Segment E′ needed for the total synthesis of (−)-kazusamycin A.     

A chiral poly(para-phenyleneethynylene) (PPE) derivative

We have investigated the chiroptical properties of novel PPEs containing chiral side chains. The synthesis of poly(2,5-bis[2-(S)-methylbutoxy]-1,4-phenyleneethynylene) (BMB-PPE) was achieved in a Heck-type aryl-aryl cross coupling (M _n = 10 000, D_p = 40). The very good solubility of BMB-PPE allows for a detailed study of its chiroptical properties. Our studies demonstrate that the bisignated CD spectra of BMB-PPE are associated with an intermolecular aggregation phenomena.     

A stereoselective synthesis of the C(3)-C(13) and C(14)-C(24) fragments of macrolactin A

Synthetic studies towards(he C(3)-C(13)and C(14)-C(24)segments(3,4)of the potent antiviral and antitumor compound macrolactin A(1)are presented.Compound 3 was constructed via a convergent and facile approach,exploiting Wittig olefination to generate the sensitive E,Z-diene moiety.Compound 4 was synthesized from the chiral-pod derived sul-fone 39a via an o-alkylation-desulfonation reaction sequence.Cu(Ⅱ)-catalyzed coupling of a Grignard reagent with an al-lylic bromide and Julia olefination were also investigated for the preparation of compound 4.     

Structural Control of (1)A(2u)-to-(3)A(2u) Intersystem Crossing in Diplatinum(II,II) Complexes

Analysis of variable-temperature fluorescence quantum yield and lifetime data for per(difluoroboro)tetrakis(pyrophosphito)diplatinate(II) ([Pt(2)(μ-P(2)O(5)(BF(2))(2))(4)](4-), abbreviated Pt(pop-BF(2))), yields a radiative decay rate (k(r) = 1.7 × 10(8) s(-1)) an order of magnitude greater than that of the parent complex, Pt(pop). Its temperature-independent and activated intersystem crossing (ISC) pathways are at least 18 and 142 times slower than those of Pt(pop) [ISC activation energies: 2230 cm(-1) for Pt(pop-BF(2)); 1190 cm(-1) for Pt(pop)]. The slowdown in the temperature-independent ISC channel is attributed to two factors: (1) reduced spin-orbit coupling between the (1)A(2u) state and the mediating triplet(s), owing to increases of LMCT energies relative to the excited singlet; and (2) diminished access to solvent, which for Pt(pop) facilitates dissipation of the excess energy into solvent vibrational modes. The dramatic increase in E(a) is attributed to increased P-O-P framework rigidity, which impedes symmetry-lowering distortions, in particular asymmetric vibrations in the Pt(2)(P-O-P)(4) core that would allow direct (1)A(2u)-(3)A(2u) spin-orbit coupling.     

A chlorine-substituted boro-adamantane (BCl)6(CH)4

Thermal degradation of 1,2-bis(dichloroboryl)ethane gives low yields of a white solid (BCl)₆(CH)₄ which has a hexaboro-adamantane structure. Substitution of the chlorine atoms by bromine or methyl occurs on treatment with BBr₃ and Sn(CH₃)₄, respectively.     

Amide (A)–thioamide (T) interconversions using Ph3SiSH (A to T) and Ph3SnOH (T to A) reagents

Ph₃SiSH transforms amides to thioamides and Ph₃SnOH performs the reverse process, with the concomitant formation of Ph₃SiOH (or Ph₃SiOSiPh₃) and Ph₃SnSSnPh₃, respectively. The chemistry is a delightful illustration of the oxophilicity of silicon compared to the thiophilicity of tin and occurs under relatively mild conditions, and for amide to thioamide transformation requires no amide activation. The chemistry is in accord with available data for Si? (S)(O), Sn? (O)(S) and C?(O)(S) bond energies. Copyright © 2016 John Wiley & Sons, Ltd.     

Total synthesis of (-)-bafilomycin A(1)

A highly stereoselective total synthesis of (-)-bafilomycin A(1), the naturally occurring enantiomer of this potent vacuolar ATPase inhibitor, is described. The synthesis features the highly stereoselective aldol reaction of methyl ketone 8b and aldehyde 60c and a Suzuki cross-coupling reaction of the highly functionalized advanced intermediates 12 and 39. Vinyl iodide 12 was synthesized by a 14-step sequence starting from the readily available beta-alkoxy aldehyde 14, while the vinylboronic acid component 39 was synthesized by a nine-step sequence from beta-hydroxy-alpha-methyl butyrate 44 via a sequence involving the alpha-methoxypropargylation of chiral aldehyde 49 with the alpha-methoxypropargylstannane reagent 54. Syntheses of fragments 12 and 39 also feature diastereoselective double asymmetric crotylboration reactions to set several of the critical stereocenters. The Suzuki cross-coupling of 12 and 39 provided seco ester 40, which following conversion to the seco acid underwent smooth macrolactonization to give 41. The success of the macrocyclization required that C(7)-OH be unprotected. The Mukaiyama aldol reaction between aldehyde 60c and the TMS enol ether generated from 8b provided aldol 65 with high diastereoselectivity. Finally, all silicon protecting groups were removed by treatment of the penultimate intermediate 65 with TAS-F (tris(dimethylamino)sulfonium difluorotrimethylsilicate), thereby completing the total synthesis of (-)-bafilomycin A(1).     

B(2)A(')-X(2)A(') detection of vibrationally excited HCO produced by the O((3)P)+C(2)H(4) reaction

The distribution of rotational and vibrational energy in HCO produced by the O((3)P)+C(2)H(4) reaction has been measured using laser-induced fluorescence detection via the B(2)A(')-X(2)A(') transition. Over a detection wavelength range of 248-290 nm, our experiments have shown that HCO is formed in both the ground state and in at least six vibrationally excited states with up to two quanta of energy in the C-O stretch and the bending mode. Dispersed fluorescence experiments were conducted to positively assign all of the HCO vibrational bands. The experiments confirmed that many bands, including the B(000)-X(000) band, are affected by overlap with other HCO bands. Spectral modeling was used to separate the contributions of overlapping HCO B-X bands and to determine a nascent HCO rotational temperature of approximately 600 K, corresponding to approximately 6% of the total energy from the O((3)P)+C(2)H(4) reaction. HCO vibrational distributions were determined for two different average collision energies and were fit with vibrational temperatures of 1850+/-80 K and 2000+/-100 K, corresponding to approximately 15% of the total energy. The observed Boltzmann distribution of vibrational energy in HCO indicates that HCO and CH(3) are formed by the dissociation of an energized intermediate complex.     

A synthesis of (±)-cryptojaponol and (±)-taxodione

A new method for the synthesis of highly substituted catechols involving the decarboxylation of an α,β-epoxyenone was developed and employed in a synthesis of two diterpenes, cryptojaponol and taxodione.     

A Three-dimensional Neodymium(III)-potassium(I) Coordination Polymer

The title compound [NdK(btec)(H2O)2]n 1 was synthesized via the hydrothermal reaction of Zn(OAc)2·H2O, Nd(NO3)3 and KOH with 1,2,4,5-benzenetetra-carboxylic acid (H4btec), and characterized by elemental analysis and infrared spectra.The crystal of 1 crystallizes in monoclinic, space group P21/c with a = 8.9023(3), b = 7.8954(1), c = 17.6249(5)A, β = 91.857(1)o, V = 1238.16(6) -3, Z = 4, C10H6KNdO10, Mr = 469.49, Dc = 2.519 g/cm3, F(000) = 900 and μ(MoKα) = 4.585 mm-1.The final R = 0.0404 and wR = 0.0832 for 2197 observed reflections with I > 2σ(I) and R = 0.0431 and wR = 0.0854 for all data.X-ray diffraction reveals that the btec ligand serves as a (16-bridging ligand to link the Nd(III) and K(I) atoms into a three-dimensional coordination polymer.Photoluminescent investigation shows that the title compound displays strong emission in the blue region, which may be attributed to an intraligand emission state.     

A Three-dimensional Neodymium（Ⅲ）- potassium（Ⅰ） Coordination Polymer

The title compound [NdK（btec）（H2O）2]n 1 was synthesized via the hydrothermal reaction of Zn（OAc）E·H2O, Nd（NO3）3 and KOH with 1,2,4,5-benzenetetra-carboxylic acid （H4btec）, and characterized by elemental analysis and infrared spectra. The crystal of 1 crystallizes in monoclinic, space group P21/c with a = 8.9023（3）, b = 7.8954（1）, c = 17.6249（5）A,β= 91.857（1）°, V= 1238.16（6）A^3, Z = 4, C10H6KNdO10, Mr= 469.49, Dc = 2.519 g/cm^3, F（000） = 900 andμ（MoKa） = 4.585 mm^-1. The final R = 0.0404 and wR = 0.0832 for 2197 observed reflections with I 〉 2σ（I） and R = 0.0431 and wR = 0.0854 for all data. X-ray diffraction reveals that the btec ligand serves as a μ16-bridging ligand to link the Nd（Ⅲ） and K（Ⅰ） atoms into a three-dimensional coordination polymer. Photoluminescent investigation shows that the title compound displays strong emission in the blue region, which may be attributed to an intraligand emission state.