Coupling Reactions and Coupling−Alkylations of Thiophenecarbaldehydes Promoted by Samarium Diiodide

The coupling reactions of 2-thiophenecarbaldehyde with aromatic or aliphatic aldehydes were promoted by samarium diiodide in the presence of hexamethylphosphoramide to give C-5 hydroxyalkylation products. The coupling reactions of 3-thiophenecarbaldehyde occurred at C-2, and the subsequent alkylations occurred at the sulfur atom, accompanied by a concurrent opening of the thiophene ring to afford γ-lactols. Double hydroxyalkylations of 2- and 3-thiophenecarbaldehydes were also carried out under appropriate reaction conditions. Synthetic applications of these thiophenecarbonyl coupling products were demonstrated, for example, by elaboration to furans, butenolides, and thiophene-fused polycyclic compounds

Synthesis of Ferrocenyl Alkenes, Dienes, and Enynes via Samarium Diiodide Promoted Tandem Addition and Dehydration of Ferrocenyl Carbonyls with Halides

A practical method for preparation of ferrocenyl alkenes, dienes, and enynes from ferrocenyl carbonyls was explored. A one-pot operation using samarium diiodide to promote the condensation reactions of ferrocenecarboxaldehyde, acetylferrocene, benzoylferrocene, and butanoylferrocene with benzyl bromides, allyl bromide, propargyl bromide, and 1-bromo-3-chlorobutane gave the olefinic products in very high yields. The condensation reactions were also achieved by using catalytic amounts of SmI2 with magnesium to regenerate the divalent samarium reducing agent

Microwave-Assisted One-Pot Tandem Reactions for Direct Conversion of Primary Alcohols and Aldehydes to Triazines and Tetrazoles in Aqueous Media

A series of primary alcohols and aldehydes were treated with iodine in ammonia water under microwave irradiation to give the intermediate nitriles, which without isolation underwent [2 + 3] cycloadditions with dicyandiamide and sodium azide to afford high yields of the corresponding triazines and tetrazoles, including the α-amino- and dipeptidyl tetrazoles in high optical purity

Preparation of Optically Active Tertiary Alcohols by Enzymatic Methods. Application to the Synthesis of Drugs and Natural Products

By the catalysis of AK or porcine pancreas lipases, 3-iodo-2-phenyl-1,2-propanediol, 1-(hydroxymethyl)-1-phenyloxirane, 2-(iodomethyl)-4-phenyl-3-butyne-1,2-diol, 2-(iodomethyl)-4-(trimethylsilyl)-3-butyne-1,2-diol, and 5,5-dimethyl-2-(iodomethyl)-3-hexyne-1,2-diol were resolved in very high enantioselectivities (E ≥ 153). The obtained enantiomerically pure or optically enriched compounds, containing an iodo atom, an oxirane moiety, or an alkynyl group, are versatile building blocks for the synthesis of chiral azido diols, sulfanyl diols, cyano diols, the side chain of a vitamin D3 metabolite, the ω-chain of a prostaglandin analog, and an aggregation pheromone (1S,5R)-(−)-frontalin. Models based on the consideration of the importance of size, distance, and electron effect are proposed to interpret the observed stereospecificity in the enzymatic reactions. Thus, the lipase-catalyzed reactions of 1,1-disubstituted 1,2-diols occurred efficiently at the primary hydroxyl groups while the enantioselectivity was controlled by the tertiary carbinyl centers

Total Synthesis of Anti-Influenza Agents Zanamivir and Zanaphosphor via Asymmetric Aza-Henry Reaction

The potent anti-influenza agents, zanamivir and its phosphonate congener, are synthesized by using a nitro group as the latent amino group at C4 for asymmetric aza-Henry reaction with a chiral sulfinylimine, which is derived from inexpensive d-glucono-δ-lactone to establish the essential nitrogen-containing substituent at C5. This method provides an efficient way to construct the densely substituted dihydropyran core of zanamivir and zanaphosphor without using the hazardous azide reagent

Synthesis of [3]Ferrocenophanes via Samarium Diiodide Promoted Reductive Cyclizations of 1,1‘-Dicinnamoylferrocenes

A series of 1,1‘-dicinnamoylferrocenes were converted to the corresponding [3]ferrocenophane diols (4a−e) in a stereoselective manner by using samarium diiodide to effect the intramolecular coupling reaction, aldol reaction, and reduction in one-pot operation. The major reaction pathway might be derived from a samarium chelated transition state (IA) having the moieties of s-cis enone and (Z)-enolate. A solid-state structure of such [3]ferrocenophane diol product showed that the cyclopentadienyl groups were in an eclipsed orientation and slightly tilted

Stereoselective Synthesis of δ-Lactones from 5-Oxoalkanals via One-Pot Sequential Acetalization, Tishchenko Reaction, and Lactonization by Cooperative Catalysis of Samarium Ion and Mercaptan

By the synergistic catalysis of samarium ion and mercaptan, a series of 5-oxoalkanals was converted to (substituted) δ-lactones in efficient and stereoselective manners. This one-pot procedure comprises a sequence of acetalization, Tishchenko reaction and lactonization. The deliberative use of mercaptan, by comparison with alcohol, is advantageous to facilitate the catalytic cycle. The reaction mechanism and stereochemistry are proposed and supported by some experimental evidence. Such samarium ion/mercaptan cocatalyzed reactions show the feature of remote control, which is applicable to the asymmetric synthesis of optically active δ-lactones. This study also demonstrates the synthesis of two insect pheromones, (2S,5R)-2-methylhexanolide and (R)-hexadecanolide, as examples of a new protocol for asymmetric reduction of long-chain aliphatic ketones

Use of Ketene Dithioacetal as a Latent Carboxylic Acid in the Macrolactonization Applicable to the Synthesis of Dilactonic Pyrrolizidine Alkaloids

Acid 5a (or 5b) bearing the ketene dithioacetal moiety functioned as an equivalent of a dicarboxylic acid. Use of the ketene dithioacetal in the formation of 11-membered dilactones is demonstrated. Compound 5a (or 5b) was converted to an acid imidazolide which reacted regioselectively with retronecine at the allylic position. Mild acidic hydrolysis of the ketene dithioacetal moiety led to a thioester, which underwent macrocyclization with the secondary hydroxyl group mediated by silver(I) trifluoroacetate to give derivatives of the pyrrolizidine alkaloids

Asymmetric Addition of Trimethylsilyl Cyanide to Benzaldehydes Catalyzed by Samarium(III) Chloride and Chiral Phosphorus(V) Reagents

Asymmetric Addition of Trimethylsilyl Cyanide to Benzaldehydes Catalyzed by Samarium(III) Chloride and Chiral Phosphorus(V) Reagent

Coupling Reactions and Coupling−Alkylations of Thiophenecarbaldehydes Promoted by Samarium Diiodide

The coupling reactions of 2-thiophenecarbaldehyde with aromatic or aliphatic aldehydes were promoted by samarium diiodide in the presence of hexamethylphosphoramide to give C-5 hydroxyalkylation products. The coupling reactions of 3-thiophenecarbaldehyde occurred at C-2, and the subsequent alkylations occurred at the sulfur atom, accompanied by a concurrent opening of the thiophene ring to afford γ-lactols. Double hydroxyalkylations of 2- and 3-thiophenecarbaldehydes were also carried out under appropriate reaction conditions. Synthetic applications of these thiophenecarbonyl coupling products were demonstrated, for example, by elaboration to furans, butenolides, and thiophene-fused polycyclic compounds