Total synthesis of (+)-13-deoxytedanolide

In this communication we describe the first total synthesis of (+)-13-deoxytedanolide, an architecturally complex marine macrolide possessing significant antitumor activity. The cornerstone of the synthesis comprises a highly convergent dithiane coupling used to construct the carbon skeleton, followed by a novel use of the Evans-Tishchenko reduction to oxidize the C(1) aldehyde to an ester in the presence of the oxidatively labile dithiane.     

Spongipyran synthetic studies. Evolution of a scalable total synthesis of (+)-spongistatin 1

Three syntheses of the architecturally complex, cytotoxic marine macrolide (+)-spongistatin 1 (1) are reported. Highlights of the first-generation synthesis include: use of a dithiane multicomponent linchpin coupling tactic for construction of the AB and CD spiroketals, and their union via a highly selective Evans boron-mediated aldol reaction en route to an ABCD aldehyde; introduction of the C(44)-C(51) side chain via a Lewis acid-mediated ring opening of a glucal epoxide with an allylstannane to assemble the EF subunit; and final fragment union via Wittig coupling of the ABCD and EF subunits to form the C(28)-C(29) olefin, followed by regioselective Yamaguchi macrolactonization and global deprotection. The second- and third-generation syntheses, designed with the goal of accessing 1 g of (+)-spongistatin 1 (1), maintain both the first-generation strategy for the ABCD aldehyde and final fragment union, while incorporating two more efficient approaches for construction of the EF Wittig salt. The latter combine the original chelation-controlled dithiane union of the E- and F-ring progenitors with application of a highly efficient cyanohydrin alkylation to append the F-ring side chain, in conjunction with two independent tactics to access the F-ring pyran. The first F-ring synthesis showcases a Petasis-Ferrier union/rearrangement protocol to access tetrahydropyrans, permitting the preparation of 750 mg of the EF Wittig salt, which in turn was converted to 80 mg of (+)-spongistatin 1, while the second F-ring strategy, incorporates an organocatalytic aldol reaction as the key construct, permitting completion of 1.009 g of totally synthetic (+)-spongistatin 1 (1). A brief analysis of the three syntheses alongside our earlier synthesis of (+)-spongistatin 2 is also presented.     

Multicomponent linchpin couplings. Reaction of dithiane anions with terminal epoxides, epichlorohydrin, and vinyl epoxides: efficient, rapid, and stereocontrolled assembly of advanced fragments for complex molecule synthesis

The development, application, and advantages of a one-flask multicomponent dithiane linchpin coupling protocol, over the more conventional stepwise addition of dithiane anions to electrophiles leading to the rapid, efficient, and stereocontrolled assembly of highly functionalized intermediates for complex molecule synthesis, are described. Competent electrophiles include terminal epoxides, epichlorohydrin, and vinyl epoxides. High chemoselectivity can be achieved with epichlorohydrin and vinyl epoxides. For vinyl epoxides, the steric nature of the dithiane anion is critical; sterically unencumbered dithiane anions afford S(N)2 adducts, whereas encumbered anions lead primarily to SN2' adducts. Mechanistic studies demonstrate that the SN2' process occurs via syn addition to the vinyl epoxide. Integration of the multicomponent tactic with epichlorohydrin and vinyl epoxides permits the higher-order union of four and five components.     

Carbolithiation of substituted stilbenes and styrenes with dithianyllithiums

Carbolithiation of a range of substituted stilbenes and styrenes with dithianyllithiums is described, leading to the rapid, efficient and stereocontrolled assembly of highly functionalized dithiane intermediates for acyl-equivalents synthesis.     

Synthesis of the bis-spiroacetal core of the antimitotic agent spirastrellolide B

The spirastrellolides are a family of potent antimitotic agents isolated from the marine sponge Spirastrella coccinea . Synthetic studies toward the DEF bis-spiroacetal core of spirastrellolide B are reported. A modular approach was pursued by the use of two dithiane disconnections to enable a highly convergent synthesis. The ease of lithiation and nucleophilicity of these 2-substituted-1,3-dithianes were investigated during the course of the synthesis, and the alkylations were found to proceed most efficiently at elevated temperatures. Formation of the [5,6,6]-bis-spiroacetal ring system was achieved via a double dithiane deprotection/spiroacetalization strategy.     

(+)-Rimocidin synthetic studies. Construction of an advanced C(1-18) polyol fragment

[structure: see text] The synthesis of an appropriately functionalized advanced C(1-18) polyol fragment of the mycosamine-glycosylated polyene macrolide, (+)-rimocidin (1), has been achieved in a highly efficient manner. Highlights of the strategy include the S(N)2/S(N)2' addition of dithiane anions to vinyl epoxides and the multicomponent linchpin union of 2-TBS-1,3-dithiane with two advanced epoxides.     

Enantioselective Addition of a 2‐Alkoxycarbonyl‐1,3‐dithiane to Imines Catalyzed by a Bis(guanidino)iminophosphorane Organosuperbase

A chiral bis(guanidino)iminophosphorane catalyzes enantioselective addition reactions of a 1,3‐dithiane derivative as a pronucleophile. The chiral uncharged organosuperbase facilitates the addition of benzyloxycarbonyl‐1,3‐dithiane to aromatic N‐Boc‐protected imines to provide optically active α‐amino‐1,3‐dithiane derivatives, which are valuable versatile building blocks in organic synthesis.     

Stereocontrolled and convergent total synthesis of amphidinolide T3

Stereocontrolled and convergent total synthesis of amphidinolide T3 has been described. A retrosynthetic scheme was constructed that led to the recognition of readily available and enantiomerically related compounds as starting materials for the total synthesis of amphidinolide T3. Thus, the two key building blocks 6 and 7 were defined as subtargets and synthesized in optically active forms. The C1-C12 fragment 6 was derived from commercially available D-glutamic acid or its synthetically equivalent (R)-5-hydroxymethyltetrahydrofuran-2-one 16 as starting material involving highly diastereoselective asymmetric allylation as a key step. The C13-C21 fragment 7 was efficiently synthesized in high yield through the dithiane coupling of the segment 10 and iodide 11, followed by subsequent deprotection and Petasis olefination. Eventually, assembly of the fragment aldehyde 6 and dithiane 7 along with C-C bond formation, a two-step oxidation-reduction sequence, selective macrolactonization, and functional transformation furnished the convergent total and formal synthesis of amphidinolide T3 and T4, and this approach also provides a flexible and practical synthesis of amphidinolide T macrolides.     

Catalyst-free conjugated addition of thiols to alpha,beta-unsaturated carbonyl compounds in water

[reaction: see text] Catalyst-free conjugate addition of thiols to alpha,beta-unsaturated carbonyl compounds in water is reported. beta-Sulfido carbonyl compounds were formed at room temperature, in short times and with excellent chemoselectivity. Competitive dithiane/dithiolane formation, transesterification, and ester cleavage were not observed. Water played a dual role in simultaneously activating the alpha,beta-unsaturated carbonyl compound and the thiol. This new methodology constitutes an easy, highly efficient, and green synthesis of beta-sulfido carbonyl compounds.     

A chiron approach to the total synthesis of (+)-aculeatin D

A synthesis of natural aculeatin D has been achieved, with the key stereogenic centers taken from inexpensive and readily available D-xylose. In elaboration of D-xylose into a desired form readily applicable in synthesis a previously misinterpreted and overlooked abnormal selectivity in hydroxyl protection was noticed and exploited. Protocols were developed for monotosylation of a triol insoluble in CH2Cl2 and "freezing" the less stable isomer (aculeatin D) at the PIFA-mediated oxidative spirocyclization, respectively. An unexplained deprotonation at a benzyl protecting group by a thermodynamically more stable dithiane carbanion in the literature was also addressed.     

分子设计合成高折光指数的光学树脂(Ⅲ)MMDMA的合成及其共聚树脂的制备

采用盐酸/硫脲法合成了2-巯基甲基-1,4-二硫杂环己烷(MMD),利用反滴碱液的低温相转移催化技术合成了2-甲基丙烯酰硫基甲基-1,4-二硫杂环己烷(MMDMA),讨论了MMD合成过程中的结构变化,研究了MMDMA的共聚性能,合成了折光指数高、色散能力低的新型光学树脂.     

7-N,7'-N'-(1",2"-Dithianyl-3",6"-dimethylenyl)bismitomycin C: synthesis and nucleophilic activation of a dimeric mitomycin

Dimeric alkylating agents that modify complementary DNA strands have engendered significant interest. We have prepared the novel dimeric mitomycin, 7-N,7'-N'-(1",2"-dithianyl-3",6"-dimethylenyl)bismitomycin C (9), in which the mitomycins are bridged by a dithiane unit. Dimer 9, like the clinically tested acyclic disulfides KW-2149 (3) and BMS-181174 (4), was designed to activate under nucleophilic and reductive conditions. Successive nucleophile-mediated disulfide cleavage transformations of 9 are expected to generate thiol species ideally positioned to render the two mitomycin systems vulnerable to nucleophilic attack and permit DNA interstrand cross-link formation. The dithiane linker, strategically positioned between the two mitomycins, distinguished 9 from 3 and 4. Nucleophilic activation of this cyclic disulfide permitted both activated mitomycins to remain tethered to one another. We report the synthesis of 9, and show that the nucleophile Et(3)P markedly enhances the activation and consumption of 9, compared with the reference compound 7-N, 7"-N'-(cyclohexanyl-trans-1",4"-dimethylenyl)bismitomycin C (27). We further demonstrated that provides higher levels of DNA interstrand cross-links than either the dimeric reference compounds, and 7-N,7-N'-(2",5"-dihydroxy-1",6"-hexanediyl)bismitomycin C (28), or the monomeric mitomycins, 1 and 3, when Et(3)P is added to solutions containing EcoRI-linearized pBR322 DNA.     

Fluorescent coumarinyldithiane as a selective chemodosimeter for mercury(II) ion in aqueous solution

A coumarin-based dithiane (1) was synthesized for the selective detection of Hg²⁺ with respect to dual chromo- and fluorogenic changing events in an aqueous solution by the mercury-promoted transformation of a dithiane group into an aldehyde functional unit. The Hg²⁺-selective response of the chemodosimeter was clearly observed in aqueous buffer as well as in human blood plasma medium.     

二茂铁基α—二酮合成的新途径

本文报道根据Corey和Seebach“羰基反应活性逆转”原理合成二茂铁基α-二酮的新途径。用锂化二茂铁基二噻烷与一个酯反应,再经HgCl_2-CdCO_3水解得到标题化合物。共合成16种酰基二茂铁基二噻烷和13种二茂铁基α-二酮化合物。除两种外,其余均为新二茂铁衍生物。所有产物的结构都由元素分析、IR和~1H NMR谱确定。本文讨论了反应中二茂铁衍生物在结构及性质上的特点和产物的IR和~1H NMR谱。     

Enantioselective formal total synthesis of the antitumor macrolide bryostatin 7

A new enantioselective synthesis of Masamune's AB fragment (1) for bryostatin 7 is described. Key steps in the new route include a Meerwein-Ponndorf-Verley reduction to set the O(7) stereocenter and an alkylative union between the dithiane 6 and iodide 5 to construct the C(9)-C(10) bond. Because we have previously published a synthesis of Masamune's C-ring phenyl sulfone 2, our new route to 1 constitutes a formal total synthesis of bryostatin 7; it also corrects the previously reported spectral data for 1 in CDCl3.     

Precision ADMET polyolefins containing dithiane: Synthesis,thermal properties,and macromolecular transformation

1,3‐Dithiane and its derivatives are widely used as powerful acyl anion equivalent to a range of useful transformations that are needed in the synthesis of natural products. In this work, a series of polyolefins containing pendant dithiane groups have been designed and synthesized via acyclic diene metathesis polymerization (ADMET) polymerization and subsequent hydrogenation. The structures of these polymers were characterized by ¹H NMR, ¹³C NMR, and FT‐IR, and successful incorporation of the dithiane groups was proved. With different contents of the dithiane moieties, these ADMET polymers exhibited distinct thermal properties different from each other as evidenced by differential scanning calorimetry and thermal gravimetric analysis. The dithiane units in the ADMET polymer with 20 methylene carbons between the adjacent dithiane groups were transformed into thiol groups via reaction with Bu₃SnH. This work provided a convenient route to synthesize polyethylene with pendant thiol groups that are evenly distributed in the chain. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2468–2475     

Acyl furans from cyclohexane-1,3-diones – A synthesis of hibiscone C

A direct route to acyl furans was developed using dithiane anion addition followed by deprotection/aromatization. This led to an efficient synthesis of hibiscone C.     

A general approach to the synthesis of enantiopure 19-nor-Vitamin D(3) and its C-2 phosphate analogs prepared from cyclohexadienyl sulfone

A synthesis of enantiopure 19-nor-Vitamin D(3) and its C-2 substituted cyclic phosphate analogs is achieved via in situ trapping of an α-sulfonyl anion with a CD-ring allyl chloride and 1,2-eliminative desulfonylation exploiting the basic properties of TBAF. The A-ring is prepared via anti-selective dithiane addition to vinyl sulfone and LiBH(4) mediated sequential bis reduction of an epoxy vinyl sulfone.     

Synthesis of fully substituted polyhydroxylated pyrrolizidines via Cope-House cyclization

Total synthesis of the proposed structure of (-)-hyacinthacine C(5) and its epimers at C6 and C7 is described. A key step of the synthesis was the construction of the bicyclic pyrrolizidine system by means of a nucleophilic addition of a dithiane to a cyclic nitrone followed by a Cope-House cyclization.