Stetter

Conversion of aldehydes to ketones via cyanohydrin derivatives (ethers) by alkylation or Michael addition also used with sdyl ethers, dialtylamlnonitnies (see also Stetter reaction). 

The hydrolysis of 2-adamantanecarbonitrile with hydrogen bromide in acetic acid provides a useful route to 2-adamantanecarboxylic acid (m.p. 143-144°), which the submitters obtained in 95% yield. Stetter and Tillmans reported a yield of 62% starting with impure 2-adaman-tanecarbonitrile. 

The only tetrasubstituted furans that have been prepared using the Feist-Benary reaction are substituted tetrahydrobenzofurans and octahydrodibenzofurans. This strategy was pioneered by Stetter and Chatterjea and applied in a series of total syntheses by Magnus. Stetter demonstrated that 1,3-cyclohexanedione (30) can act as the P-dicarbonyl component and readily combines with either 3-bromo-2-ketobutyric (29) acid or ethyl 2-chloroacetoacetate (32) in the presence of potassium hydroxide to yield tetrahydrobenzofuran derivatives 31 and 33, respectively. ... 

The Paal synthesis of thiophenes from 1,4-diketones, 4-ketoaldehydes and 1,4-dialdehydes has found great use in the synthesis of medicinally active compounds, polymers, liquid crystals and other important materials. Furthermore, the discovery of the catalyzed nucleophilic 1,4-conjugate addition of aldehydes, known as the Stetter reaction (Eq. 5.4.1), has enabled widespread use of the Paal thiophene synthesis, by providing 1,4-diketones from readily available starting materials. ... 

An interesting application of the Paal thiophene synthesis was documented for the synthesis of a polystyrene-oligothiophene-polystyrene copolymer. In the Stetter reaction of aldehyde 13 and P-dimethylaminoketone 14, in situ generation of the a,p-unsaturated ketone preceded nucleophilic 1,4-conjugate addition by the acyl anion... 

Structure-activity studies of 5,6,7,8-tetrahdyro-5,5,8,8-tetramethyl-2-quinoxaline derivatives necessitated the preparation of thiophene-containing compound 17. Stetter conditions using thiazolium salt 20 as catalyst resulted in the preparation of 1,4-diketone 21 from 18 and 19. Condensation of 21 with phosphorus pentasulfide followed by saponification resulted in 17. In this fashion, the authors replaced the amide linker of parent compound 22 with the rigid thiophene moiety. 

Novel compounds for use in liquid crystal displays have been prepared via the Stetter procedure followed by Paal thiophene formation with Lawesson s reagent. Thus... 

Stetter and ReischP described the preparation of 2,6-diphonyl-P5Tylium perchlorate (57) from l,5-diphenyl-2-penten-4-yn-l-one (56a) and concentrated sulfuric acid in the cold, followed hy perchloric acid, in 60% 5rield. The process may involve hydration to a 1,5-enedione, or an ion 56b related to 52, and valence tautomerism. 

The triazole 76, which is more accurately portrayed as the nucleophilic carbene structure 76a, acts as a formyl anion equivalent by reaction with alkyl halides and subsequent reductive cleavage to give aldehydes as shown (75TL1889). The benzoin reaction may be considered as resulting in the net addition of a benzoyl anion to a benzaldehyde, and the chiral triazolium salt 77 has been reported to be an efficient asymmetric catalyst for this, giving the products (/ )-ArCH(OH)COAr, in up to 86% e.e. (96HCA1217). In the closely related intramolecular Stetter reaction e.e.s of up to 74% were obtained (96HCA1899). 

J. Stetter (ed.), Herbicides Inhibiting Branched Chain Amino Acids Biosynthesis. Recent Development [Chemistry of Plant Protection, Vol. 10], Springer-Verlag, Berlin, 1994. 

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