General synthetic approach to bicyclo[9.3.0]tetradecenone: a versatile intermediate to clavulactone and clavirolides

An efficient and stereoselective approach to the bicyclo[9.3.0]tetradecenone core structure of clavulactone starting from readily and abundantly available 2-methyl-1,3-cyclopentandione employing microbial desymmetrization and cyanohydrin alkylation as the key steps is described. The synthetic route described herein is applicable to the syntheses of the core structures of Clavirolides A-F.     

群柱虫内酯官能团化的C2-C10片段的立体选择性合成

本文以廉价的消旋甲基戊二酸酐为起始原料,完成了具有抗肿瘤活性的海洋天然产物群柱虫内酯（Clavulactone）官能团化的C2-C10片段的立体选择性合成。使用的关键方法包括不对称去对称化获得光学纯手性孤立甲基,和RCM方法构建顺式烯烃。该片段的获得为群柱虫内酯的全合成提供了基础。     

Enantioselective total synthesis of marine diterpenoid clavulactone

The key steps in the synthesis of clavulactone are formation of an enantiopure cyclopentane precursor by epoxide rearrangement and intramolecular carbonyl-ene reaction, construction of the 3,4-dihydro-2H-pyran ring by intermolecular hetero-Diels-Alder reaction, closure of the eleven-membered ring, and finally generation of the lactone functionality by chemoselective allylic C(sp(3))-H oxidation.     

Fluoride-mediated elimination of allyl sulfones: application to the synthesis of a 2,4-dimethyl-A-ring vitamin D3 analogue

A coupling strategy for the synthesis of 2,4-dimethyl-1α,25(OH)(2)D(3) is achieved which involves methylation of a pro-A ring vinyl sulfone and in situ traping of the allyl sulfonyl anion with a CD ring allyl chloride. TBAF-promoted 1,2-eliminative desulfonylation and concomitant silyl ether deprotection gives the vitamin D(3) analogue.     

Binolam-AlCl: a two-centre catalyst for the synthesis of enantioenriched cyanohydrin O-phosphates

The enantioselective synthesis of cyanohydrin O‐phosphates by using in situ generated bifunctional catalysts (R)‐ or (S)‐3,3′‐bis(diethylaminomethyl)‐1,1′‐binaphthol–aluminium chloride (binolam–AlCl) is reported. The reaction, which can be described as an overall cyano‐O‐phosphorylation of aldehydes, has a wide scope and applicability. Evidence is also provided, including ab initio and DFT calculations, in support of supported by the Lewis acid/Brønsted base (LABB) dual role of the catalyst in inducing first the key enantioselective hydrocyanation, which is then followed by O‐phosphorylation. A brief screening of the synthetic usefulness of the resulting cyanohydrin O‐phosphates unveiles some interesting applications. Among them, chemoselective hydrolysis, reduction and palladium‐catalysed nucleophilic allyl substitution, thereby leading to enantiomerically enriched α‐O‐phosphorylated α‐hydroxy esters, β‐amino alcohols and γ‐cyanoallyl alcohols, respectively. Naturally occurring (?)‐tembamide and (?)‐aegeline are synthesised accordingly.     

Synthesis of the ring system of phomactin D using a Suzuki macrocyclization

[reaction: see text]The ring system of phomactin D was synthesized in racemic form in an efficient manner from 2,3-dimethylcyclohexanone. Notable transformations include (1) an alkylation of the enolate of a vinylogous thiolester to install a quaternary stereocenter, (2) a conjugate addition of cyanide to an alpha,beta-unsaturated aldehyde, (3) the formation of a Weinreb amide directly from a cyanohydrin, and (4) an intramolecular Pd-mediated Suzuki coupling of a B-alkyl-9-BBN derivative and a vinyl iodide to form the macrocyclic ring.     

Reaction of allylsilanes and allylstannanes with alkynes catalyzed by electrophilic late transition metal chlorides

The intramolecular reaction of allylsilanes and allylstannanes with alkynes proceeds catalytically in the presence of Pt(II), Pd(II), Ru(II), and Au(III) chlorides. Although more limited, AgOTf also catalyzes the cyclization. Usually, PtCl2 as the catalyst in methanol or acetone gives the best results. The reaction proceeds by exo attack of the allyl nucleophile on the alkyne to form five- or six-membered ring carbocycles. The reaction generally proceeds with anti stereoselectivity. However, a terminally substituted trimethylsilyl derivative reacts by a syn-type addition. The intermediate alkenylpalladium complex has been trapped with allyl chloride to form an allylated derivative with an additional carbon-carbon bond.     

The chemistry of acylals. 3. Cyanohydrin esters from acylals with cyanide reagents

[reaction: see text] When treated with KCN in DMSO at room temperature, acylals from aliphatic aldehydes gave the corresponding cyanohydrin esters in good to excellent yields. Acylals from aromatic aldehydes were less reactive and gave several byproducts in addition to fair yields of cyanohydrin under the same conditions. Trimethylsilyl cyanide mixed with titanium(IV) chloride afforded cyanohydrin esters in good to excellent yields from both aliphatic and aromatic aldehydes.     

Synthesis and transformations of 6,6,7,7-tetramethyl-2-quinuclidone

6,6,7,7-Tetramethyl-2-quinuclidone was synthesized, and its differences from the usual amides were shown. It enters into three types of chemical reactions: 1) the N-CO bond is broken under the influence of protic nucleophilic agents (water, alcohols, amines, hydroxylamine, and hydrazines), and nucleophilic agents are acylated by the (2,2,6,6-tetramethyl-4-piperidyl)-acetic acid residue; 2) the N-C(CH₃)₂ bond is broken by reaction with nucleophilic agents in aprotic media (phenyllithium in ether, PCl₅ in benzene, acetone cyanohydrin, and LiAlH₄ in ether) to form 4-substituted 6,6-dimethyl-2-piperidones; 3) reactions with the preservation of the quinuclidine ring occur on treatment with electrophilic reagents (hydrogen chloride and methyl iodide) in aprotic solvents and during reduction.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 378–384, March, 1971.     

Intramolecular methylation of an allyl sulfone via lithium alkoxyaluminate; application to the enantioselective synthesis of the CD ring of vitamin D3

Alcohol-directed intramolecular methylation of an enantiopure allyl sulfone using AlMe(3) provides a trans-hydrindane CD ring alcohol. The substrate cis-CD ring allyl sulfone alcohol is prepared via intramolecular allyl sulfonyl anion addition to aldehyde using Ba(OH)(2).     

1,4-Asymmetric Induction in the Chromium(II)- and Indium-Mediated Coupling of Allyl Bromides to Aldehydes

A series of allyl bromides bearing an ethereal stereogenic substituent at C-2 were synthesized from methyl acrylate. These were coupled with a range of aldehydes under chromium(II) chloride-mediated conditions to afford syn-4-alkoxyalkan-1-ols in good yield and diastereoselectivity. The effect of altering the nature of the ethereal group and alkyl substituent upon the diastereoselectivity of the reaction was also investigated. The relative stereochemistry was proved by X-ray structure analysis. The work was extended to replace the chromium(II) chloride with indium metal, and this also afforded syn-4-alkoxyalkan-1-ols in good yield and diastereoselectivity.     

改进的1,3-缩水-2,4-二-氧-苄基-β-L-鼠李糖及1,3——缩水-2,4,6-三-氧-苄基-β-D-甘露糖的合成

用相应二丁基锡络合物对α-L-鼠李糖烯丙基苷及α-D-甘露糖烯丙基苷进行选择性3-氧-烯丙基化. 用(Ph~3P)~3RhCl催化脱烯丙基并苄基化得到相应的苄基化1,3-二醇. 再进行乙酰化,氯化,接着进行关环反应,得到1,3-缩水苄基内醚糖.     

Enantio- and diastereoselective additions to aldehydes using the bifunctional reagent 2-(chloromethyl)-3-(tributylstannyl)propene: application to a synthesis of the C16-C27 segment of bryostatin 1

[reaction: see text] Reactions of the bifunctional allylstannane 2-(chloromethyl)-3-(tributylstannyl)propene with aldehydes have been examined. These generally occur in high yields using Lewis acid promoters and the products can be isolated and purified without incident. Good yields and high enantioselectivities are also realized in catalytic asymmetric allylations (CAA reactions) using the previously described BITIP catalyst system. Protection of the free hydroxyl can be accomplished without cyclization to the derived tetrahydrofuran, although this transformation is also facile. The utility of the incorporated allyl chloride functionality allows for the obvious use of such products in reactions with nucleophiles. Use of these products in a less obvious connective strategy is demonstrated in the synthesis of the C12-C27 segment of bryostatin 1 where a connective, or "lynchpin", double-allylation process was employed. The beta-hydroxy allyl chloride obtained from an initial chelation-controlled allylation of aldehyde 16 was converted to allylstannane 19 and applied in a second allylation reaction, thus allowing for a highly convergent synthesis of the bryostatin C ring backbone in a stereoselective fashion.     

Synthesis and Halocyclization of 5-Allyl-2-benzyl(allyl)sulfanyl-6-methylpyrimidin-4(3H)-ones

Russian Journal of Organic Chemistry - Alkylation of 5-allyl-6-methyl-2-thiouracil with benzyl chloride and allyl bromide afforded 2-benzyl(allyl)sulfanyl-5-allyl-6-methylpyrimidin-4(3H)-ones....     

Copolymerization of acrylamide with allyl-acrylate quaternary ammonium monomers

A series of copolymers of N,N-morpholine-N-2-(ethoxycarbonyl)allyl allyl ammonium chloride, N,N-morpholine-N-2-(ethoxycarbonyl)allyl allyl ammonium bromide, N,N-piperidyl-N-2-(ethoxycarbonyl)allyl allyl ammonium chloride, N,N-morpholine-N-2-(t-butoxycarbonyl)allyl allyl ammonium bromide and diallyldimethylammonium chloride (DADMAC) with acrylamide (AAm) were prepared in water at 50-56°C using 2,2'-azo-bis(2-amidinopropane)dihydrochloride (V-50). The ethyl ester monomers showed high cyclization efficiencies during copolymerizations. The tert-butyl ester derivatives showed high cross-linking tendencies. The molar fractions of allyl-acrylate monomers in the AAm: allyl-acrylate copolymers were higher than the one of DADMAC in the AAm:DADMAC copolymers. The intrinsic viscosities of the copolymers measured in 0.09 M NaCl ranged from 2.5 to 7.5 dL/g.     

Reaction of Substituted 2-Allylthiopyrimidin-4(3H)-ones with Sulfenyl Chlorides

Reaction of substituted 2-allylthiopyrimidin-4(3H)-ones with p-nitrobenzosulfenyl chloride gives the products of addition at the allyl moiety, while the reaction with 2-benzothiazolyl sulfenyl chloride yields thiazolidinopyrimidines with an angular structure.     

Synthesis of 1,3-dioxolane derivatives

Chloral cyanomethylhemiacetal is converted to 2-trichloromethyl-4-imino-1,3-dioxolane under the influence of hydrogen chloride or pyridine. Acetone cyanohydrin reacts with chloral to give 2-trichloromethyl-4-imino-5,5-dimethyl-1,3-dioxolane, the hydrochloride of which in water gives 2-trichloromethyl-4-oxo-5,5-dimethyl-1,3-dioxolane.     

Cationic polymerization of 4-methyl-1,3-dioxene-4 and copolymerization with tetrahydrofuran

A new monomer, 4-methyl-1,3-dioxene-4 was synthesized from allyl chloride and paraformaldehyde. The monomer was polymerized at room temperature or ?78°C. by boron trifluoride etherate catalyst, and the structure of the obtained polymer was determined by infrared, nuclear magnetic resonance spectra, and chemical analysis. It was ascertained that the polymerization process proceeded through a ring-opening mechanism at the dioxane ring. In the presence of tetrahydrofuran, the polymerization of 4-methyl-1–1,3-dioxene-4 led to copolymer. The mechanism of the copolymerization is described in detail.     

Formal synthesis of (-)-apicularen A

[reaction: see text] A formal synthesis of (-)-apicularen A has been completed. The synthesis features a cyanohydrin acetonide coupling as a convergent approach to the C9-C18 segment and an intramolecular Diels-Alder addition sequence to create both the 10-membered macrocycle and the aromatic ring.     

An efficient and facile one-pot synthesis of cyanohydrin esters from carbonyl compounds catalyzed by iron(III) chloride

A variety of cyanohydrin esters were readily prepared from carbonyl compounds with trimethylsilyl cyanide and acid anhydride under the influence of a catalytic amount of iron(III) chloride in a convenient one-pot procedure.