Vinyl selenides reduction

Several other transannular lactonizations and reductions have been reported to proceed in high overall yields. Also other acid derivatives, such as amides and esters, cyclize to form lactones. Alkynoic acids have been lactonized to y-alkylidene-y-lactones in good yield, e.g. the conversion of (31) to (32 equation 29). Unfortunately the vinyl selenide product can isomerize from ( ) to (Z) in a secondary process. Analogous lactam formation is also known. Unsaturated amides, when cyclized with benzenese-lenenyl halides, produce good yields of lactams or iminolactones depending upon the alkene utilized. The amide (33) cyclizes to the iminolactone (34), producing a mixture of stereoisomers (65 35 Scheme 5). The amide (35) is cyclized to lactam (36) in moderate yield. 

Aithough some reactions, such as the transformation of -hydroxyalkyi selenides to 3-haloalkyl selenides (Scheme 161, b) or to vinyl selenides, enones (Scheme 161, a,a-dihalocyclopropanes (Scheme 162, f) or 3-hydroxya]kyl halides (Scheme 161, h Scheme 162, g), - have bera occasionally described or found oniy with specific types of -hydroxyalkyi seienides, especialiy those having a strained ring [e.g. their transformation to aliyi selenides (Scheme 163, b), - 1-selenocyclobutenes (Scheme 163, c) - and cyclobutanones (Scheme 163, f),i2.is9.i ).i63] others are far more general. This is particulariy the case of their reductions to alcohols (Scheme 161, a Scheme 162, a Scheme 163, a Scheme 164, a Scheme 165, ay.tss,i89,246 alkenes (Scheme 161, c Scheme 162, c Scheme 163, d Scheme 164, c Scheme 165, a Scheme 166, their transformation to allyi alcohols... 

Unfortunately, the appeal of solid phase extractions on small scale fades as the scale increases due to the cost and inconvenience of using large amounts of fluorous silica gel. Here, modified techniques to reduce the tedium of repeated extractions are attractive. For example, Crich has recently introduced the minimally fluorous selenide C6Fi3CH2CH2C6H4SeH[171. This selenol is added in catalytic quantities to tin hydride reductions of reactive aryl and vinyl radicals. The high reducing capacity of the aryl selenide suppresses undesired reactions of product radicals without suppressing the reactions of the aryl and vinyl radicals themselves. After the reaction is complete, the selenol can be recovered by a modified continuous extraction procedure. 

---