d-Glucosamine trimethylene dithioacetal derivatives: formation of six- and seven-membered ring amino carbasugars. Synthesis of (–)-calystegine B3,

The Corey-Seebach Reagent in the 21st Century: A Review

The Corey-Seebach reagent plays an important role in organic synthesis because of its broad synthetic applications. The Corey-Seebach reagent is formed by the reaction of an aldehyde or a ketone with 1,3-propane-dithiol under acidic conditions, followed by deprotonation with n-butyllithium. A large variety of natural products (alkaloids, terpenoids, and polyketides) can be accessed successfully by utilizing this reagent. This review article focuses on the recent contributions (post-2006) of the Corey-Seebach reagent towards the total synthesis of natural products such as alkaloids (lycoplanine A, diterpenoid alkaloids, etc.), terpenoids (bisnorditerpene, totarol, etc.), polyketide (ambruticin J, biakamides, etc.), and heterocycles such as rodocaine and substituted pyridines, as well and their applications towards important organic synthesis.

Current Synthetic Approaches to the Synthesis of Carbasugars from Non-Carbohydrate Sources

Carbasugars are a group of carbohydrate derivatives in which the ring oxygen is replaced by a methylene group, producing a molecule with a nearly identical structure but highly different behavior. Over time, this definition has been extended to include other unsaturated cyclohexenols and carba-, di-, and polysaccharides. Such molecules can be found in bacterial strains and the human body, acting as neurotransmitters (e.g., inositol trisphosphate). In science, there are a wide range of research areas that are affected by, and involve, carbasugars, such as studies on enzyme inhibition, lectin-binding, and even HIV and cancer treatment. In this review article, different methods for synthesizing carbasugars, their derivatives, and similar cyclohexanes presenting comparable characteristics are summarized and evaluated, utilizing diverse starting materials and synthetic procedures.

Silver(i)-catalyzed addition of pyridine-N-oxides to alkynes: a practical approach for N-alkenoxypyridinium salts

A smooth catalytic approach to N-alkenoxypyridinium salts by using pyridine-N-oxides as the nucleophilic partner with alkynes under acidic conditions has been developed. This method uses different Ag(i) salts, with 5% AgOAc being the most efficient, to provide an efficient, practical and alternative way to obtain valuable N-alkenoxypyridinium salts with good to excellent yields (up to 93%).

Concise synthesis of calystegines B2 and B3via intramolecular Nozaki-Hiyama-Kishi reaction

The key step in the concise syntheses of calystegine B2 and its C-2 epimer calystegine B3 was the construction of cycloheptanone 8via an intramolecular Nozaki-Hiyama-Kishi (NHK) reaction of 9, an aldehyde containing a Z-vinyl iodide. Vinyl iodide 9 was obtained by the Stork olefination of aldehyde 10, derived from carbohydrate starting materials. Calystegines B2 (3) and B3 (4) were synthesized from d-xylose and l-arabinose derivatives respectively in 11 steps in excellent overall yields (27% and 19%).

1-(N,N-diisopropylcarbamoyloxy)-1-tosyl-1-alkenes--a2d1 synthons via tandem umpolung

1-(N,N-diisopropylcarbamoyloxy)-1-tosyl-alkenes have been developed as an a(2)d(1) synthon via tandem umpolung. Upon addition of Grignard reagents and further quench by carbonyl compounds, this synthon produces alpha,alpha'-branched-alpha'-oxygenated ketones. Strategically, this widely applicable method installs respectively a carbanion unit and a carbonyl unit formally onto the alpha-carbon and the carbonyl center of an aldehyde in one-pot.