1,2-Allenyl selenides

One of the rare applications of selenium-substituted allenes was recently reported by Ma et al. [182]. The allenyl selenide 352 undergoes an iodohydroxylation or iodo-amination, depending on the amount of water used, leading to the formation of allyl alcohol 353 and allylacetamide 354 (Scheme 8.97). When the reaction is performed with 12-16 equiv. of water, allyl alcohol 353 is exclusively formed, whereas the use of 1 equiv. of water exclusively provides the amide 354 in 64% yield. 

Metalloamides are suitable for the synthesis of 1-metallovinyl aryl selenides (Scheme 44) and 1-metalloallenyl phenyl selenides (Scheme 45) from the corresponding vinyl or allenyl selenides. The synthesis of the latter organometallics is even more conveniently achieved by metallation of l-phe-nylseleno-l-propyne or by a two-step, one-pot sequence of reactions fiom 2-chloroallyl phenyl selenide (Scheme 45). 

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

Epoxidation of f-butyldimethylsilyl-l-(ethoxyethoxy)allene (6) with /n-chloroperbenzoic acid leads to an a-keto acylsilane, presumably through an allene oxide intermediate (eq 6). Deprotonation of (6) at C-3 and trapping of the anion with selenium, followed by iodomethane, produces an aUenyl selenide. The reaction of this material with peracid follows a different course, leading to an acetylenic acylsilane, presumably via [2,3]-sigmatropic rearrangement of an allenyl selenide (eq 6) ... 

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. 

Iodoalkylation of 1,2-allenyl sulfides or selenides, ArXCH=C=CH2 (X = S or Se), with I2 in MeCN-ROH (20 1) has been shown to afford (Z)-3-alkoxy-2-iodopropenyl (g) sulfides or selenides, ArXCH=C(I)-CH2OR, in high stereoselectivity and moderate to good yields.43... 

Furthermore, allenyl phenyl selenides have been prepared by alkylation of 1-lithioallenyl phenyl selenide, itself produc on metallation of phenyl 1-propynyl selenide or of allenyl phenyl selenide - (Scheme 42). 1-Lithioallenyl phenyl selenide has poorer nucleophilic properties than that of a-seleno-allyllithiums, since the reaction of the former with 2-phenyl-1-bromoethane gives predominantly styrene, whereas the latter leads to products of substitution in good yield. ... 

Many total syntheses take advantage of the temporary introduction of a sulfide or a sulfone group. As illustrated in Scheme 5, an allenyl sulfone is a key intermediate in the synthesis of brassinolide reported by Back [31a]. It is obtained through sequential addition of TsSePh, base-promoted migration of the double bond, and oxidative elimination of the phenyl selenide. The addition of EtSH to the... 

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