Synthesis of the N-((1E)-alkenyl)-(2Z,4Z)-heptadienamide side chain of salicylihalamide A and apicularens A and B

Decarboxylative Enamide Synthesis from Carboxylic Acid and Alkenyl Isocyanate

Herein, we reported a protocol to access the enamide via employing carboxylic acid and alkenyl isocyanate as the precursors promoted by DMAP without involving any metal catalysts and dehydration reagents. This protocol is simple and practical and tolerates numerous functional groups. Considering the simplicity, the ready availability of both starting materials, and the significance of the enamides, we expect that this reaction will find broad application.

Addition of lithium carbenoids to isocyanates: a direct access to synthetically useful N-substituted 2-haloacetamides

The addition of lithium carbenoids to isocyanates provides a versatile access to N-substituted 2-haloacetamides: the reaction tolerates the presence of variously functionalized substituents on the nitrogen atom, including sterically demanding ones and reactive halogens. No erosion of the enantiopurity was observed in the case of optically active isocyanates. One of the substrates prepared has been employed in Charette's type chemoselective addition of a Grignard reagent to access an α-chloroketone.

Synthesis of sterically hindered enamides via a Ti-mediated condensation of amides with aldehydes and ketones

The first TiCl(4)-mediated condensation of secondary amides with aldehydes and ketones has been achieved. The reaction proceeds at room temperature and is complete within 5 h in most cases. The optimized procedure used 5 equiv of an amine base hinting that the in situ activation of both the amide and the Lewis acid is required. The reaction affords polysubstituted (E)-enamides.

Synthesis of the Eastern Portion of Ajudazol A Based on Stille Coupling and Double Acetylene Carbocupration

[structure: see text] A strategy for the synthesis of ajudazol A, an unusual, pharmacologically active metabolite from myxobacteria, based on the Stille cross-coupling of a 2-stannyl-oxazole with a vinyl iodide unit is described; the vinyl halide unit containing a (Z,Z)-diene was prepared in one pot by the double acetylene carbocupration of a functionalized alkyl cuprate followed by trapping with 2,3-dibromopropene.

CuI/N,N-Dimethylglycine-Catalyzed Coupling of Vinyl Halides with Amides or Carbamates

The CuI-catalyzed coupling reaction of vinyl halides with amides or carbamates proceeds well at room temperature to 80 degrees C in dioxane to give enamides using N,N-dimethylglycine as the promoter and Cs(2)CO(3) as the base. The geometry of the C-C double bond is retained during the reaction course. [reaction: see text]

Divergent and Stereocontrolled Synthesis of the Enamide Side Chains of Oximidines I/II/III, Salicylihalamides A/B, Lobatamides A/D, and CJ-12,950

[reaction: see text] A unified strategy for the divergent and stereocontrolled introduction of the (E)- and (Z)-enamide side-chains of oximidines I, II, and III, salicylihalamides A and B, lobatamides A and D, and CJ-12,950 is detailed. The synthesis relied on the copper-promoted C-N coupling of (E)- and (Z)-vinyl iodides with a protected maleimide hemiaminal followed by deprotection and reaction of the resulting (E)- or (Z)-enelactam hemiaminals with O-methylhydroxylamine or propylidenetriphenylphosphorane.

Copper-Catalyzed Coupling of Amides and Carbamates with Vinyl Halides

[reaction: see text] A general and efficient copper-catalyzed method for the amidation of vinyl bromides and iodides has been developed. This protocol uses a combination of 5 mol % copper iodide and 20 mol % N,N'-dimethyl ethylenediamine. Substrates bearing ester, silyl ether, and amino groups were successfully coupled under the reaction conditions. The double bond geometry of the vinyl halides was retained under the reaction conditions.

Lobatamide C: total synthesis, stereochemical assignment, preparation of simplified analogues, and V-ATPase inhibition studies

The total synthesis and stereochemical assignment of the potent antitumor macrolide lobatamide C, as well as synthesis of simplified lobatamide analogues, is reported. Cu(I)-mediated enamide formation methodology has been developed to prepare the highly unsaturated enamide side chain of the natural product and analogues. A key fragment coupling employs base-mediated esterification of a beta-hydroxy acid and a salicylate cyanomethyl ester. Three additional stereoisomers of lobatamide C have been prepared using related synthetic routes. The stereochemistry at C8, C11, and C15 of lobatamide C was assigned by comparison of stereoisomers and X-ray analysis of a crystalline derivative. Synthetic lobatamide C, stereoisomers, and simplified analogues have been evaluated for inhibition of bovine chromaffin granule membrane V-ATPase. The salicylate phenol, enamide NH, and ortho-substitution of the salicylate ester have been shown to be important for V-ATPase inhibitory activity.

Formal total synthesis of salicylihalamides A and B

An efficient synthesis of the macrolactone 3 of the salicylihalamides in 10 linear steps from alkene 6 is described. The key steps involved a Stille coupling between the chiral stannane 5 and benzyl bromide 4, which produced alkene 15 in good yield, and subsequent base-induced macrolactonization then gave compound 3. Macrolactone 3 was then converted into the known salicylihalamide A intermediate 18 in a three-step sequence. Compound 3 was also converted into another known salicylihalamide A and B intermediate 23 in a five-step sequence.

Total synthesis of (-)-salicylihalamide

A concise total synthesis of the potent cytotoxic marine natural products salicylihalamide A and B (la, b) is reported. Key steps of our approach were the asymmetric hydrogenation reactions of beta-keto esters 18 and 32 catalyzed by [((S)-BINAP)Ru-Cl2]2. NEt3 and the cyclization of the macrolide core by ring closing olefin metathesis (RCM) using the "second-generation" ruthenium carbene complex 24 as the catalyst which bears an imidazol-2-ylidene ligand. The EIZ ratio obtained in this macrocyclization reaction was determined by the protecting groups at the remote phenolic OH group of the cyclization precursor. The elaboration of the resulting cycloalkene 37 into the final target involved a CrCl2-mediated synthesis of vinyliodide 49 which, after deprotection, did undergo a copper-catalyzed cross-coupling process with the (Z,Z)-configurated carboxamide 42 to form the labile enamide moiety of 1. Compound 42 was derived from a palladium-catalyzed Negishi coupling between butynylzinc chloride and 3-iodoacrylate 39 followed by a Lindlar reduction of enyne 40 thus obtained and a final aminolysis of the ester group.

Asymmetric synthesis of the fully functional macrolide core of salicylihalamide: remote control of olefin geometry during RCM

A catalysis-based approach to the core region 24 of the antitumor agents salicylihalamides A and B is reported. Key steps are two asymmetric hydrogenations of beta-keto esters 13 and 16 catalyzed by [(R)-BINAP.RuCl(2)](2).NEt(3) and an RCM-based macrocyclization effected by the NHC-containing ruthenium carbene 21. The stereochemical outcome of the latter reaction is controlled by remote substituents on the phenolic OH group of the cyclization precursor 23.

Synthesis of enamides related to the salicylate antitumor macrolides using copper-mediated vinylic substitution

[formula: see text] A new approach to the assembly of enamides is described using copper(I) carboxylate-catalyzed substitution of vinyl iodides and amides. Modified reaction conditions have been developed to synthesize the O-methyloxime enamide side chains related to the natural products lobatamides A-F, oximidine I and II, and CJ-12,950.