Selenium-nucleophiles

Reaction with Selenium Nucleophiles. The reactions of selenium nucleophiles are similar to those of the sulfur nucleophiles selenophosphates can be aminoaLkylated (135). A dihydroselenazine has been obtained by reaction of diethyl ketone, elementary selenium, and ethyleneimine (136). 

As mentioned in the introduction, partially fluorinated compounds are highly useful, however methods for their synthesis are strictly limited in many cases. For example, nucleophilic substitution occurs with difficulty at the position a to a trifluoromethyl group due to its strong electron-withdrawing effect, although sulfur and selenium nucleophiles undergo such a substitution rather efficiently (Scheme 6.1). 

Like oxygen nucleophiles, phosphorus and selenium nucleophiles have been employed rarely in Michael additions to activated dienes. The reaction of phosphites with acceptor-substituted dienes was studied by several Russian groups116-118 again, 1,6-adducts and 2 1 addition products were formed (equation 37). The acid-catalyzed reaction of selenourea with sorbic acid was also reported to provide a 1,6-addition product119 (equation 38). 

The Michael additions to 1 - 3 of a large variety of carbon, nitrogen, oxygen, sulfur and selenium nucleophiles, as well as hydride, followed by inter- or intramolecular transformations of the chlorine substituent or/and the methoxy-carbonyl fragment, offer versatile synthetic approaches to a large variety of synthetically useful and important organic molecules. 

Oxophilic phosphomum compound 47 forms from tributylphosphine (46) and the phenylselenide 45, and this then suffers nucleophilic attack by alcohol 18. The resulting free selenium nucleophile 48 displaces phosphine oxide 50 with the formation of phenylsele-nide 51. Phenylselenide 51 is oxidi/ed by hydrogen peroxide to phenylselenoxide 52, which at room temperature undergoes an elimination reaction to (-)-A9tl2)-capnellene (1). The mechanism is similar to that of the Cope elimination, proceeding via a cyclic transition state. 

NLO properties, 12, 128 organometallic complexes, 3, 318 as reaction materials, 3, 368 and selenium nucleophiles, 9, 471 surface chemistry on oxides, 12, 502 in triruthenium cyclopentadienyl clusters, 6, 799 trivalent halides, with metal carbonyl monoanions, 3, 347 Group 14 elements... 

The selenetanes that have been described in the literature have been constructed via three types of reactions. Selenetane derivatives are generally prepared via the [2+2] two-component syntheses (Schemes 8 and 9 Equations 3-7). The [1+3] two-component syntheses via the reaction of a selenium nucleophile with a three-carbon unit have been carried out (Scheme 6, and Equations 8-10, 12, and 13). One-component syntheses via rearrangement-cyclization have also been performed (Scheme 7). 

Michael reactions of a,/Uunsaturated carbonyl compounds 95 using selenium nucleophiles afford (3-seleno carbonyl derivatives 96 usually in good yields.1 This reaction has been used as a protection strategy for the a,/ -unsaturated double bond, because an oxidative elimination of the selenium moiety in 96 leads to the regeneration of the double bond.176 Such reactions have also been applied to natural product synthesis177 and in asymmetric versions of Michael additions in the presence of alkaloids as chiral ligands (Scheme 22).178... 

Also widely employed are organoselenium compounds containing group 14 elements. Phenyl trimethylsilyl selenide 102 can be easily prepared from diphenyl diselenide 8 and is a good source for selenium nucleophiles (Scheme 24). In the presence of methanol selenols are generated for use in Michael reactions or in ring-... 

Figure 4 Versatile selenium nucleophiles for organic synthesis.

Keywords. Selenium, Nucleophilic reactions, Selenimn bonded to main group elements. Asymmetric synthesis. Solid-phase synthesis... 

The opening of activated cyclopropanes with nitrogen nucleophiles has been widely applied to the synthesis of pynolizidine and pyrroline alkaloids by Danishefsky this subject has been reviewed. A number of pyrroline annulations have been based on this principle, illustrated in equation (35a). > Similar opening can be accomplished with halides, cuprates, and sulfur or selenium nucleophiles. ... 

Reaction of electrophilic cyclopropanes with sulphur and selenium nucleophiles 526... 

I. Nucieophiiic displacement with sulfur and selenium nucleophiles... 

Sulfur and selenium nucleophiles react with organoantimony and -bismuth halides or alkoxides. Several examples are shown in equations 275 ", 276 277 and 278 . ... 

Sulfur and selenium nucleophiles react with arsenic halides, amides and alkoxides to give the corresponding substituted products as shown in equations 154 155 156 , ... 

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