Selenides, propargylic

By heating alkynyl propargyl selenides give 2-methylene-3-cyclobutene-l-selones, Scheme 29, which dimerize giving a mixture of the corresponding 1,3-diselenetanes232... 

This displacement of an allylic QH5Se group by a (CH,)3Sn group is observed also with allenyl, propargyl, and benzyl selenides, and in all cases results in the less substituted of the two possible trimethylstannyl compounds. 

Allylic metals, in propargylic alcohol alkylation, 11, 129 ir-Allylic palladium complexes, and carbocyclization, 11, 426 Allylic position, alkenes, dienes, polyenes, metallation, 9, 6 Allylic selenides, [2,3]sigmatropic rearrangement, 9, 481 Allylic substitution reactions for C-N bonds via amination... 

Dibromoselenuranes 196 can be prepared from the corresponding selenides by reaction with elemental bromine. The a,/ -unsaturated ester 196 is converted into the a-bromo-/ ,7-unsaturated ester 197 by elimination of phenyl-selenenyl bromide (Scheme 58).338 Dibromoselenuranes from propargylic selenides undergo similar reactions leading to either allenes or propargylic bromides.339... 

A-allylic amines are conveniently prepared in high yields by the reaction of azides with allylindium reagents in the presence of sodium iodide at ambient temperature (Equation (74)).307 Stannylation with tributylchloro-stannane occurs exclusively at the a-carbon, yielding allyltributylstannanes (E, Z)-isomerization of the allylic double bond depends largely upon the substitution pattern on the allylic moiety (Equation (75)).26 Allyl and propargyl bromides react with diphenyl diselenides in aqueous media to give allyl and propargyl selenides (Equation (76)).308 309... 

Propargyl phenyl selenide is a versatile multifunctional acrylate synthon, as shown in Scheme 12. The (Uanion is prepared and reacted successively with an alkylating agent (R— X) and an electrophile (E ). The oxidative rearrangement of the propargylic selenoxide (35) to an allenic selenenate (36), and thence to the a-phenylselenoenone (37), forms the keystone of this synthetic method, and ovendl yields firom propargyl phenyl selenide are in the range of 38-68%. Further elaboration of (37) is possible... 

In the presence of indium, allyl bromides and propargyl bromides react smoothly with diselenides in aqueous media to give allyl and propargyl selenides, respectively, in moderate to good yields (Scheme 38 a,b) [74]. By app-... 

Decomposition of dihalogenoselenuranes 167, derived from propargylic selenides, resulted in the formation of 1,3-substituted l,3-dihalo-2-phenyl-selenopropanes 168 and 169 as well as 1-substituted 1,2,3-trihalopropanes 170 and 171 as shown in Scheme 21 177]. 

AJlylic and propargylic selenides seem to be more acidic. In the i nylseleno series, for example, the synthesis of diose compounds bearing an alkyl substituent on die caibanibnic center hais been already achieved with LDA and does not require the use of stronger bases (Schemes 16-20). In the mediylseleno series, however, die use of LiTMP (Scheme 16, h Scheme 18, c and d) or KDA (Scheme 18, e compared with c and d) is often needed. 

Isomerization of propargyl to allenyl selenide. Isomerization of allenyl to 1-propynyl selenide. pA = 17.1, pATbSe= 18.6... 

Alkylation ofa-thio- and a-seleno-alkyllithiums Alkylation ofa-thio- and a-seleno-benzylmetals Alkylation ofa-thio- and a-seleno-allylmetals Alkylation ofa-thio- and a-seleno-propargylic metal derivatives Alkylation of a-metallovinyl sulfides and selenides... 

Propargylic sulfides " and selenides have been metallated with n-butyllithium and lithium amide respectively, and allylated or alkylated selectively at the propargylic position (Scheme 34) with primary and secondary alkyl halides. - ... 

Phenyl propargyl sulfide " and selenide are rapidly deprotonated by 2 equiv. of base. The resulting dilithio derivatives react at their allylic rather than at their alkynic carbon centers (Scheme 34, entries c and d). Reduction of the sulfides allows the synthesis of 1,5-enynes (Scheme 34, entry b), whereas oxidation of the selenides leads to a-phenylseleno-a,P-unsaturated carbonyl compounds (Scheme 34, entry... 

Alkyl, benzyl, allyl and propargyl sulfides and selenides arising from the alkylation of the corresponding heterosubstituted organometallics have been used in several interesting transformations. These transformations take advantage of the easy reduction of the C—S and of the C—Se bond which can be carried... 

Reaction with diselenides. Organoindiums derived from allyl or propargyl halides and a-halo ketones react with diselenides to afford unsaturated selenides and a-seleno ketones, respectively. 

Propargyl selenides, such as phenyl propargyl selenide, are readily deprotonated by LDA at -78 °C to give a stable dilithium reagent which is of synthetic value in preparing disubstituted propargyl selenides. 

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