Very large, soluble endohedral fullerenes in the series La2C90 to La2C138: isolation and crystallographic characterization of La2@D5(450)-C100

An extensive series of soluble dilanthanum endohedral fullerenes that extends from La(2)C(90) to La(2)C(138) has been discovered. The most abundant of these, the nanotubular La(2)@D(5)(450)-C(100), has been isolated in pure form and characterized by single-crystal X-ray diffraction.     

Studies directed toward the total synthesis of azaspiracid: stereoselective construction of C(1)-C(12), C(13)-C(19), and C(21)-C(25) fragments

[reaction: see text] The efficient entry to the C(1)-C(12), C(13)-C(19), and C(21)-C(25) fragments of azaspiracid is outlined. The C(1)-C(12) portion is constructed using a key asymmetric allenyl borane addition to the corresponding alpha,beta-unsaturated aldehyde. The synthesis of the C(13)-C(19) portion utilizes an Evans asymmetric alkylation followed by Sharpless asymmetric dihydroxylation. In addition, a novel solution to the mismatched effects of a neighboring chiral oxazolidinone during a Sharpless dihydroxylation is detailed.     

Total synthesis of scytophycin C. 1. Stereoselective syntheses of the C(1)-C(18) segment and the C(19)-C(31) segment

[structure: see text] Stereoselective total synthesis of scytophycin C, a marine 22-membered macrolide displaying potent activity against a variety of human carcinoma cell lines, has been reported in which the polypropionate structure bearing contiguous asymmetric centers was stereospecifically constructed by using new acyclic stereocontrol. This paper describes stereoselective syntheses of the C(1)-C(18) segment (Segment A) including a trans-disubstituted dihydropyran ring and the C(19)-C(31) segment (Segment B) having eight stereogenic centers.     

Synthesis of C(1)-C(11) oxygen-bridged pregnanes

A general procedure for the synthesis of 1α,11α- and 1β,11α-epoxysteroids is described, using an intramolecular remote functionalization reaction involving the photolysis of 11α-hydroxysteroids in the presence of diacetoxyiodobenzene and iodine. Three 1,11-epoxypregnanes were prepared, two of them (compounds 10 and 14) are conformationally constrained analogues of steroidal hormones, compound 13 is a synthetic precursor of neurosteroids.     

Halichondrin B: synthesis of the C(1)-C(15) subunit

A short and efficient synthesis of the C(1)-C(15) subunit of halichondrin B in its natural configuration is described. The polycyclic caged ketal 3, containing nine asymmetric centers, is prepared in 14 steps from alpha-D-glucoheptonic acid gamma-lactone (7). Key steps in the two similar routes described include EtMgBr-promoted pinacol ring expansions of hydroxy mesylates 23 and 34, intramolecular Michael additions of 29 and 37, and a one-pot, HF-induced conversion of 4 to 3involving in situ silyl ether cleavage, acetal hydrolysis, Michael addition, and caged ketal formation. Alternative protocols for carbinol inversion at C(11), one early and one late in the synthetic sequence, are also described.     

Isolation of three isomers of Sm@C84 and X-ray crystallographic characterization of Sm@D(3d)(19)-C84 and Sm@C2(13)-C84

Three isomers with the composition Sm@C(84) were isolated from carbon soot obtained by electric arc vaporization of carbon rods doped with Sm(2)O(3). These isomers were labeled Sm@C(84)(I), Sm@C(84)(II), and Sm@C(84)(III) in order of their elution times during chromatography on a Buckyprep column with toluene as the eluent. Analysis of the structures by single-crystal X-ray diffraction on cocrystals formed with Ni(II)(octaethylporphyrin) reveals the identities of two of the isomers: Sm@C(84)(I) is Sm@C(2)(13)-C(84), and Sm@C(84)(III) is Sm@ D(3d)(19)-C(84). Sm@C(84)(II) can be identified as Sm@C(2)(11)-C(84) on the basis of the similarity of its UV/vis/NIR spectrum with that of Yb@C(2)(11)-C(84), whose carbon cage has been characterized by (13)C NMR spectroscopy. Comparison of the three Sm@C(84) isomers identified in this project with two prior reports of the preparation and isolation of isomers of Sm@C(84) indicate that five different Sm@C(84) isomers have been found and that the source of samarium used for the generation of fullerene soot is important in determining which of these isomers form.     

X-ray crystallographic proof of the isomer D2-C84(5) as trifluoromethylated and chlorinated derivatives, C84(CF3)16, C84Cl20, and C84Cl32

Minor isomer comes forward: Minor isomer C(84)(5) has been captured by high temperature trifluoromethylation with CF(3)I and chlorination with VCl(4). The compounds C(84)(CF(3))(16), C(84)Cl(20), and C(84)(5)Cl(32) were investigated by X-ray crystallography providing the first direct proof of the cage connectivity of D(2)-C(84)(5). The D(2)-C(84)(5)Cl(32) molecule (see figure; C grey, Cl green) contains two flattened, pyrene-like substructures on opposite poles of the cage resulting in its drum-like shape.     

Capturing C90 Isomers as CF3 Derivatives: C90(30)(CF3)14, C90(35)(CF3)16/18, and C90(45)(CF3)16/18

High‐temperature trifluoromethylation of a C₉₀ isomeric mixture with CF₃I followed by HPLC separation of C₉₀(CF₃)_n isomers resulted in the isolation of several individual C₉₀(CF₃)_14?18 compounds. Single crystal X‐ray diffraction with the use of synchrotron radiation resulted in the structure determination of C₉₀(30)(CF₃)₁₄, C₉₀(35)(CF₃)_16/18, and C₉₀(45)(CF₃)_16/18. Their addition patterns are discussed and compared with the known isomers C₉₀(30)(CF₃)₁₈ and C₉₀(35)(CF₃)₁₄, respectively. The presence of the most stable C₉₀ isomer, C₉₀(45), in the fullerene soot has been confirmed for the first time.     

Synthesis of macrolide antibiotics. 16. Synthesis of erythronolides A and B by a coupling scheme of (C5-C9) + (C3-C4) + (C1-C2) + (C10) + (C11-C13) fragments and synthesis of the C5-C9 fragment

Conclusions A synthesis of a C⁵-C⁹-fragment common to erythronolides A and B was carried out starting from levoglucosan.For previous communications, see [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 674–680, March, 1989.     

The polyol domain of amphidinol 3. A stereoselective synthesis of the entire C(1)-C(30) sector

[structure: see text] The richly oxygenated C(1)-C(30) polyol segment of amphidinol 3 has been synthesized in protected form. Incorporated in this long chain are 10 of the 25 stereogenic centers housed in the target. The asymmetric pathway that has been developed is based on the efficient union of three independently prepared subunits.     

具有Oh对称性的C32和C32H32结构和稳定性研究

本文通过对具有Oh对称性的C32和C32H32分子应用STO-3G基组从头计算的几何构型优化和HF计算结果的分析, 讨论了它们的结构特性, 分析了它们分子轨道之间的关系, 讨论了C32和C32H32的结构稳定性, 指出C32H32可能是一种潜在的立体碳烷。     

Stereoselective syntheses of the C(1)-C(9) fragment of amphidinolide C

Stereoselective syntheses of the C(1)-C(9) fragments 18 and 28 of amphidinolide C have been developed. The first-generation sequence involves a diastereoselective chelate-controlled [3 + 2]-annulation reaction of 6 and 7, while the second-generation synthesis involves an intramolecular hetero-Michael cyclization of 8.     

Iron Sulfido Derivatives of the Fullerenes C(60) and C(70)

Toluene solutions of C(60) react upon UV irradiation with Fe(2)S(2)(CO)(6) to give C(60)[S(2)Fe(2)(CO)(6)](n)() where n = 1-6. C(60)[S(2)Fe(2)(CO)(6)](n)() where n = 1-3 have been isolated and characterized. Crystallographic studies of C(60)S(2)Fe(2)(CO)(6) show that the S-S bond of the Fe(2) reagent is cleaved to give a dithiolate with idealized C(2)(v)() symmetry. The addition occurred at a 6,6 fusion, and the metrical details show that the Fe(2) portion of the molecule resembles C(2)H(4)S(2)Fe(2)(CO)(6). IR spectroscopic measurements indicate that the Fe(2)(CO)(6) subunits in the multiple-addition species (n > 1) interact only weakly. UV-vis spectra of the adducts show a shift to shorter wavelength with addition of each S(2)Fe(2)(CO)(6) unit. Photoaddition of the phosphine complex Fe(2)S(2)(CO)(5)(PPh(3)) to C(60) gave C(60)[S(2)Fe(2)(CO)(5)(PPh(3))](n)(), where n = 1-3. (31)P{(1)H} NMR studies show that the double adduct consists of multiple isomers. Photoaddition of Fe(2)S(2)(CO)(6) to C(70) gave a series of adducts C(70)[S(2)Fe(2)(CO)(6)](n)() where n = 1-4. HPLC analyses show one, four, and three isomers for the adducts, respectively.     

Stereoconvergent synthesis of the C1-C11 and C12-C24 fragments of (−)-macrolactin-A

Stereoconvergent syntheses of the C1-C11 and C12-C24 fragments of (−)-macrolactin-A are reported.     

Synthesis of the C8-C20 and C21-C30 segments of pectenotoxin 2

In this study, we synthesized the C8-C20 and C21-C30 segments of the diarrhetic shellfish toxin pectenotoxin 2. The C8-C20 segment was assembled from a phosphonate corresponding to the C8-C15 segment (prepared from l-malic acid in 19 steps) and an aldehyde corresponding to the C16-C20 segment (synthesized from 3-methyl-3-butenol in nine steps) by a twelve-step process including the Horner-Wadsworth-Emmons reaction, regio- and stereoselective reduction of the resulting enone, diastereoselective epoxidation, and 5-exo epoxide cleavage forming the C-ring. The C21-C30 segment was constructed in 13 steps from (S)-glycidol via a route involving E-ring formation by 5-exo epoxide cleavage and stereoselective methylation at C27 by the Evans method.     

Preparation, crystallographic characterization and theoretical study of C70(CF3)16 and C70(CF3)18

C70(CF3)16 and C70(CF3)18, the first trifluoromethylated fullerene derivatives to comprise a pair of adjacent CF3 groups, have been isolated from a mixture obtained via reaction of C70 with CF3I, characterized in a single crystal XRD study and theoretically investigated at the DFT level of theory.     

Tetrafibricin: synthesis of the C1-C13, C15-C25, and C27-C40 fragments

[structure: see text] A sequence of chemoselective cross-metathesis reactions and enantioselective allyltitanations of aldehydes has been used to prepare the C1-C13, C15-C26, and C27-C40 fragments of tetrafibricin.