Tandem Wittig – Reductive annulation decarboxylation approach for the synthesis of indole and 2-substituted indoles

A simple tandem Wittig reaction-reductive decarboxylation route is established for the synthesis of indoles from commercially available o-nitrobenzaldehydes and a stable phosphorane. The method allows access to indoles in a very fast manner without involving any metal or expensive reagents or inert atmosphere. Also 2-substituted indoles are obtained which forms an important core of many biological active compounds.     

Synthesis of β3-amino acid and peptides from D-ribose

Synthesis of new β³-amino acid, peptides and conformational analysis are reported from d-ribose, using Wittig olefination and Aza-Michael addition.     

Spongistatins: Biological activity and synthetic studies

Following the isolation from marine sponges, in 1993, of a family of related highly oxygenated macrolactones named spongistatins, altohyrtins and cinachyrolides, impressive synthetic efforts have been devoted to the synthesis of these macrolides. Their highly potent activity as cancer cells growth inhibitors combined with a fascinating and complex architecture has prompted synthetic organic chemists to develop efficient routes to these molecules. From the first total syntheses by the groups of Evans and Kishi in 1997 and 1998 which delivered milligram quantities of spongistatins/altohyrtins, further intensive studies have led to new pathways with practical solution to provide gram scale amounts of key intermediates. The present review focuses on biological properties and synthetic issues related to these marine macrolides.     

Synthesis of the mixed acetal segment of S-glyceroplasmalopsychosine

In this report the concept of converting carbohydrate to non-carbohydrate asymmetric molecules has been successfully exploited. The mixed acetal segment of glyceroplasmalopsychosine, a novel glycolipid, has been synthesized in a stereospecific manner using two simple sugar units. The glycosidation reaction between these two monosaccharides ensured the correct acetal stereocenter of the target molecule. Either olefin metathesis or heterogeneous Wittig reactions were used for constructing the long aliphatic chain of glyceroplasmalopsychosine.     

Stereoselective total synthesis of (+)-(6R,2′S)-cryptocaryalactone and (−)-(6S,2′S)-epi cryptocaryalactone

The total synthesis of (+)-(6R,2′S)-cryptocaryalactone and (−)-(6S,2′S)-epi cryptocaryalactone is reported based on stereoselective reduction of δ-hydroxy β-keto ester to install 1,3-polyol system, cis Wittig olefination, and lactonization as the key steps. The synthesis of (−)-(6S,2′S)-epi cryptocaryalactone is also reported using syn-benzylidene acetal formation and a preferential Z-Wittig olefination reaction and lactonization as the key steps.     

Synthesis of 2S-(2-hydroxyethyl)-3R-hydroxy-4S-(thymin-1-yl or adenin-9-yl)-tetrahydrofuran

Two synthetic strategies were developed to obtain isonucleosides 2a and 2b. Starting from the known compound 4, an extension of one carbon unit at sugar 6-terminal was achieved by Wittig reaction and Stannyl-desulfonylation reaction. After oxidation of the double bond, the isonucleosides with elongated side chain 2a and 2b were synthesized. For the synthesis of isonucleosides containing different bases, an epoxide intermediate approach was developed. Isonucleosides 2a and 2b were synthesized by regioselective epoxide opening reaction of 18 in good yield.     

The first entry to pyrrolo[2,3-c]quinoline-2,4(3aH,5H)-diones

Wittig olefination of 3-aminoquinoline-2,4(1H,3H)-diones 1 with ethyl (triphenylphosphoranylidene)acetate (Ph₃PCHCO₂Et) afforded (E)-3-amino-4-ethoxycarbonylmethylene-1,2,3,4-tetrahydro-2-quinolones (E)-2 and pyrrolo[2,3-c]quinoline-2,4(3aH,5H)-diones 3. An alternative approach for the synthesis of 3 via 3-bromoacetamidoquinoline-2,4(1H,3H)-diones 7, their corresponding triphenylphosphonium salts 8, and ylides A that undergo intramolecular Wittig reaction, was investigated. Under the applied reaction conditions, the phosphonium salts 8 and ylides A are so unstable that they partly decompose to 3-acetamidoquinoline-2,4(1H,3H)-diones 9 during the synthesis of 3.     

Design and synthesis of (E)-4-((3-ethyl-2,4,4-trimethylcyclohex-2-enylidene)methyl)benzoic acid

(E)-4-((3-Ethyl-2,4,4-trimethylcyclohex-2-enylidene)methyl)benzoic acid, 6, was synthesized in 87% starting from β-cyclocitral. The target compound 6 was synthesized starting from 1 via a Grignard reaction to form alcohol 2. Compound 2 was converted to Wittig salt 3 by treatment with aldehyde 4 in butyllithium and hexane at −78 °C to form ester 5. Ester 5 was saponified and, following acidification, acid 6 was isolated as white solid yield 87%.     

A Triphenylphosphine-Based Microporous Polymer for a Wittig Reaction Cycle in the Solid State

The Wittig reaction is a key step in industrial processes to synthesise large quantities of vitamin A and various other important chemicals that are used in daily life. This article presents a pathway to achieve the Wittig reaction in a solid network. A highly porous triphenylphosphine-based polymer was applied as a solid Wittig reagent that undergoes, in a multi-step cycle, in total six post-synthetic modifications. This allowed for regeneration of the solid Wittig reagent and reuse for the same reaction cycle. Of particular industrial relevance is that the newly developed material also enables a simple way of separating the product by filtration. Therefore, additional costly and difficult separation and purification steps are no longer needed.     

Dynamic NMR study of the oxaphosphetane complexation with lithium during the Wittig reaction

Dynamic NMR spectroscopy at very low temperatures (148–182 K) reveal the dynamic behavior of the (2‐tri(3‐furyl)‐3‐methyl‐4‐cyclopropenyl‐oxaphosphetane) generated during a Wittig reaction between tri(3‐furyl)ethylphosphonium iodine and cyclopropylaldehyde. The possibility of formation of different adducts between Li⁺ ions and oxaphosphetane or betainic intermediates was checked calculating the formation enthalpies using the MNDO, AM1, and PM3 semiempirical MO methods. The observed species are interpreted as oxaphosphetane complexes with lithium ions present in solution. Quantum mechanical calculations confirm the spectroscopic results. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008