Vinyl selenone, addition

Synthesis of a-Selenoalkyl Metals by Addition of Organometallics to Vinyl Selenides, Vinyl Selenoxides and Vinyl Selenones... 

Additions of various nucleophiles to vinyl selenoxides - and vinyl selenones have been described. Thus potassium hydroxide and amines add to vinyl selenones and directly produce epoxides and aziridines, respectively, whereas 3-methoxyoxetanes have been obtained from 7-hydroxy-a-alkenyl selenones and st ium methoxide (Scheme 111). ... 

Shimizu et al. prepared the cyclic ( )-vinyl ether (270) in moderate yield by an addition-fragmentation reaction of the diol (271) by treatment with sodium hydride in THF overnight. The conjugate addition of the alkoxide to the vinyl selenone generates (272), then (273), leading to bond rupture and the expulsion of phenylselenone to form (270) (Scheme 31) <84JOC1230>. 

In 2011, Marini and co-workers [49] described an organocascade for the synthesis of spirolactones from cyclic (3-ketoesters and a vinyl selenone by an enantioselective Michael addition followed by intramolecular nucleophilic substitution of the phenyl-selenoyl leaving group (Scheme 16.24). 

Michael addition of a-aryl-a-isocyanoacetates (352) to vinyl selenone (353), catalysed by the quinine derivative (351), has been reported to proceed readily at —40 °C, affording... 

In the same year, Marini and coworkers developed an interesting synthesis of spirolactones 85 based on an organocatalyzed Michael addition-cyclization reaction sequence (Scheme 10.29) [49]. tert-Butyl ketoesters 82 reacted with vinyl selenone... 

Michael addition/cyclization sequence. Angewandte Chemie International Edition, 50, 9382-9385. (b) Sternativo, S., Batistelli, B., Bagnoli, L., Santi, C., Testaferri, L., Marini, F. (2013). Synthesis of y-lactams via a domino Michael addition/cyclization reaction of vinyl selenone with substituted amides. Tetrahedron Letters, 54, 6755-6757. 

At the same time as the emergence of the vinyl sulfones as Michael acceptors in organocatalyzed conjugate additions, a new type of acceptor appeared in the form of vinyl selenones. 

Scheme 34.36 Addition of a-cyanoesters to vinyl selenone 99 and postfiinctionalizations.

Scheme 34.37 Synthesis of cyclopropanes by sequential addition to vinyl selenone and cyclization.

A highly efficient synthesis of spirolactone 110 was described by Marini et al. in 2011 [82] using the addition of cyclic 5-ketoester 111 to vinyl selenone 99 and subsequent cyclization of intermediate 112 in the presence of silica (Scheme 34.39) under mild conditions. This reaction exhibited a wide scope (selected examples are given in Scheme 34.39) but was limited to P-ketoesters with a cydopentanone core. Moreover this process could be extended to stereodivergent parallel kinetic resolution of a racemic mixture of chiral P-ketoesters with a high degree of enantioselectivity. 

For the same sequence, vinyl sulfones and vinyl selenones have appeared as new partners in organocatalyzed asymmetric conjugate addition, giving access to valuable building blocks. 

As a consequence of the selenoxide instability, the oxidation into selenones is only possible if the syn-elimination reaction becomes difficult, as in the case of strained structures. Under these conditions, the selenone is deprotonated and the a-selenonylalkyllithiums formed can react as other selenium-stabilized car-banions. It must be added that the seleninyl [PhSe(O)-] and selenonyl [PhSe(02)-j substituents behave as very good leaving groups. Vinylic selenoxides and selenones can undergo an intramolecular displacement of the selenium moiety after nucleophilic addition to the double bond under basic conditions. Cyclopropanes and oxetanes have been synthesized in this way [1,2]. 

Vinylic ether-containing Claisen rearrangement substrates may be generated using syn-elimination reactions of sulfoxides, selenoxides, and selenones. 2-(Arylsulfinyl)ethyl ethers are particularly useful substrates in these reactions because of their ready availability by nucleophilic addition of allylic alcohols to commercially available phenylsulfinylethene. Scheme 13.27 shows a typical synthetic context for this chemistry, involving the stereospecific introduction of quaternary centers from easily accessed allylic alcohol precursors." ... 

---