Synthesis of the C1–C13 fragment of eribulin mesylate

Synthesis of the C1–C13 fragment of eribulin mesylate has been accomplished. It features a highly stereoselective construction of a trans-dihydropyran framework using three key reactions: (1) Sharpless epoxidation, (2) regioselective ring opening, and (3) olefin metathesis.     

Stereoselective synthesis of C19–C27 fragment of bryostatin 11

A convergent synthesis of C19–C27 fragment (2) of bryostatin-11 is described. The key steps involved in this approach are kinetic resolution, Grignard reaction, and Sharpless dihydroxylation. AIBN catalyzed radical cyclization strategy has been used for the first time to construct the six-membered pyran system.     

Synthesis of the C8–C16 fragment of amphidinolide R

An asymmetric synthesis of the C8–C16 fragment with several stereogenic centers of amphidinolide R, is described. The key reaction, Sharpless asymmetric epoxidation has provided the basis for generation of the required stereocenters. The target fragment was accomplished in a convergent manner in nine steps (longest linear synthesis of the sequence) and 32% overall yield was obtained starting from 2-butene-1,4-diol.     

Synthesis of the C29–C37 segment of spongistatin 1

Starting from racemic 2α-methyl-8-oxabicyclo[3.2.1]oct-6-en-3-one the spongistatin E segment has been prepared in nine steps (2.3 steps per stereogenic center) with umpolung of anomeric reactivity at C37. This 3,5-syn-diol sequence completes our methodology to all stereoisomers of 3,5,7-trihydroxy heptanoic ester building blocks functionalized for α-oxyanion chemistry.     

Stereoselective synthesis of C3–C17 and C18–C34 subunits of bullatanocin utilizing α-chloro sulfide intermediates

A convergent synthesis of bullatanocin is envisaged by the union of C18–C34, C3–C17 and the butenolide subunits. The synthesis of the C3–C17 and C18–C34 subunits is disclosed that takes advantage of the chirality of tartaric acid for 1,2-asymmetric induction, chloro sulfides for carbon chain elongation and [2,3] sigmatropic shift for the preparation of 1,4-diol moiety via efficient 1,3-chirality transfer. The THF ring is elaborated by intramolecular displacement.     

Recent strategic advances for the activation of benzylic C–H bonds for the formation of C–C bonds

Alkylarenes, obtained from abundant hydrocarbon feedstock sources, are an attractive starting material for the formation of complex molecular architectures. Conventional activation strategies of the relatively inert sp³-hybridized benzylic C–H bonds usually require relatively harsh conditions and are difficult to apply to the synthesis of fine chemicals. The present review describes recent strategic advances for the activation of benzylic C–H bonds for the catalytic formation of C–C bonds. In particular, two activation methods, i.e., strategies that generate benzylic radicals or benzyl anions, are discussed.     

An improved synthesis of the C42–C52 segment of ciguatoxin 3C

In our previously reported method for the construction of the IJKLM-ring of ciguatoxin 3C (CTX3C), the lengthy synthetic process for the intermediate C42–C52 (L-ring) segment was problematic. Therefore, a new and improved procedure for the C42–C52 segment, having modified protecting groups, was developed. The new route includes a chirality transferring Ireland-Claisen rearrangement for the construction of the vicinal dimethyl branching at C47–48, a one-pot cyclization process for the establishment of the stereocenters at C45 and C46 as well as the γ-hydroxy δ-lactone framework corresponding to the L-ring, and Brown’s asymmetric crotylboration for the installation of the stereocenters at C43 and C44. The new C42–C52 segment was successfully coupled with the previously reported C32–C41 (I-ring) segment to produce the IJKLM-ring.     

Synthesis of the C38–C54 spiroketal segment of halichondrin B

Stereoselective synthesis of the C38–C54 segment of a marine metabolite halichondrin B comprising KLM and N rings with a C44 spiroketal including 10 chiral centers is described. The salient features of the synthesis are Carreira’s addition, Sharpless asymmetric dihydroxylation and double alkylation of TosMIC strategy and double vinyl coupling reactions.     

Experimental study of Fe–C–O based system above 1,000 °C

The paper deals with the study of phase transformation temperatures of the model Fe–C–O based metallic alloys in the high temperature region (above 1,000 °C). Six model alloys with graded carbon and oxygen content were prepared and studied. Temperatures of phase transitions were obtained using DTA method (differential thermal analysis). The Setaram SETSYS 18? (TG/DTA/DSC/TMA) modular experimental system was used for measurements. Influence of composition change (carbon and oxygen content) on shift of phase transformation temperatures is investigated in this paper. New original data (phase transformation temperatures) were obtained in this study. Controlled heating of the alloys was conducted at the rates of 2, 4, 7, 10, 15 and 20 °C min^?1. Comparison of the obtained experimental data with the data presented in the literature was also carried out. It follows from comparison of the obtained results with the data accessible in the literature that a lack of experimental data exists, and these available data significantly differ.     

Experimental study of Fe–C–O based system below 1000 °C

The paper deals with the study of phase transformation temperatures of Fe (Fe–C–O) based metallic alloys. Six model alloys with graded carbon and oxygen content were used for experimental investigation. Low-temperature region (<1000 °C) was the investigated area. Phase transformation temperatures were obtained using Differential thermal analysis and Setaram Setsys 18_TM laboratory system. Controlled heating was conducted at the rates of 2, 4, 7, 10, 15, 20 °C min^?1. Region of eutectoid transformation (Fe_α(C) + Fe₃C → Fe_γ(C)), alpha–gamma (Fe_α(C) → Fe_γ(C)) and transformation Fe_α(O) + Fe_0.92O → Fe_γ(O) + Fe_0.92O was studied. New original data (phase transformation temperatures) were obtained in this study. The relationship between shift of phase transformation temperatures and chemical composition (mainly carbon and oxygen content) is investigated in this paper. To achieve good approximation to the equilibrium conditions, the extrapolation of the obtained phase transformation temperatures to the zero heating rate was performed. The influence of experimental conditions (heating rate) on temperatures of phase transformations was studied as well. Comparison of the obtained experimental data with the data presented in the accessible literature and IDS calculations (Solidification Analysis Package) was carried out. It follows from literature search that there is a lack of thermo-physical and thermo-dynamical data on Fe–C–O system.     

Radical cascade reactions of unsaturated C–C bonds involving migration

During the past few years, with the rapid development of mild methods for the generation of radical species, great progress in radical cascade reactions of unsaturated C–C bonds has been made. Many radical cascade reactions involve functional groups migration, which leads structurally much more diverse, complex and valuable compounds not easily obtained through other methods. In this review, the recent achievements in unsaturated C–C bonds radical cascade reactions involving migration are summarized.     

Stereo selective synthesis of C3–C12 fragment of iriomoteolide-1a

A convergent and flexible synthetic route for the synthesis of C3–C12 fragment of iriomoteolide-1a is described. The key steps are: Mannich reaction, Keck asymmetric allylation, Sharpless asymmetric epoxidation and cross-metathesis protocol.     

Toward the stereoselective synthesis of C1–C23 fragment of spirastrellolide B

A convergent synthesis of the protected C(1)–C(23) fragment 4 of the targeted natural product spirastrellolide B is described. The key step of the synthesis is cross metathesis (CM) and TBAF promoted oxa-Michael to construct tetrahydropyran moiety.     

Concise total syntheses of Marinoquinolines A–C

The first concise total syntheses of pyrroloquinoline natural products, Marinoquinolines A–C, have been achieved in six linear steps from commercially available starting materials. The key steps were a reaction between (p-tolylsulfonyl)methylisocyanide (TosMIC) and α, β-unsaturated ester under basic condition to prepare the pyrrole moiety and Morgen-Walls reaction to construct quinoline ring.     

Synthesis of a mitomycin C–lexitropsin hybrid

We have constructed hybrid drugs where mitomycin C is linked to the N-methylpyrrole carboxamide framework present in lexitropsins. The coupling reactions leading to these products are efficient and the yields are very high. An interesting spectroscopic feature of these hybrids is the red shift observed in the UV–vis spectrum. Although DFT calculations indicate the possible existence of complexes formed during the coupling reactions, these complexes were not detected. The only species produced and isolated were the mitomycin C-mono- and bis-N-methyl pyrrole conjugates.     

Liquid–liquid equilibria of alkane (C10–C14)+octylbenzene+sulfolane

The liquid–liquid equilibria (LLE) data are presented for mixtures of alkane (C10/C12/C14)+octylbenzene+sulfolane at 323.15, 348.15 and 373.15 K. The addition of octylbenzene to sulfolane is found to increase the solubility of alkanes in the order of decane>dodecane>tetradecane. The tie line data were correlated with the well-known UNIQUAC and NRTL models. The calculated values based on the UNIQUAC model were found to be better than those based on the NRTL model. The values of selectivity and distribution coefficient were derived from the equilibrium data.     

Discovery of redox system enabling C–N–C bonds formation: Unprecedented Aza-Cannizzaro reaction

A novel reaction involving in situ redox conversion of glyoxylate esters to glycine is described. Simple starting materials and mild conditions for the synthesis of glycine derivatives probably indicate a pathway towards prebiotic chemistry. This proceeds analogous to Cannizzaro reaction involving ammonia therefore it can be termed as intramolecular Aza-Cannizzaro type reaction. This reaction is examined in detail with an aid of computational analysis to corroborate the proposed mechanism.     

Transition metals catalyzed C–C and C–O bonds formation: facile synthesis of flavans and benzoxepines

A simple and practical method has been developed based on intermolecular [Pd]-catalyzed C–C and an intramolecular [Cu]-catalyzed C–O bond formations for the synthesis of flavans and benzoxepines. Interestingly, the method is amenable for the synthesis of a wide variety of flavans and benzoxepines with dense functionalities on aromatic moieties. Significantly, flavans and benzoxepines are present as core/part-structures in many biologically active natural products.     

Gram scale synthesis of the C(1)–C(9) fragment of amphidinolide C

An allylic cis-epoxide prepared by Sharpless asymmetric epoxidation was transformed in nine steps and 41% overall yield to the cyclization precursor 4 via a key one carbon homologation. Cobalt-catalyzed aerobic oxidative cyclization of 4 gave the trans-THF in 94% yield at gram scale. Subsequent manipulations, including a Still–Gennari olefination, Sharpless asymmetric dihydroxylation, Corey–Fuchs alkynylation, and Kazmaier hydrostannylation provided the fully functionalized C(1)–C(9) fragment 2 suitable for cross-coupling. The sequence is readily scalable and provides gram quantities of 2.