Selenides homoallylic

HOMOALLYLIC ALCOHOLS B-Allyldiisopino-campheylborane. Allyl phenyl selenide. Allyltri-/i-butyltin. Chromium(II) chloride. Crotyltrimethylsilane. Diethylftributyl-stannyl)aluminum. (2R,4R)-Pentanediol. Pinacol chloromethaneboronate. Tin-Aluminum. Titanium(lV) chloride. 

Homoallylic alcohols.1 The anion (LDA) of allyl phenyl selenide reacts with a trialkylborane in THF at - 78° to form an ate complex (a) which rearranges at 0° to the complex b. An allylic rearrangement of b to c occurs at 25°. Reaction of b with an... 

In this case also the corresponding, optically active diastereoisomerical-ly pure homoallylic selenides 134 were isolated as a single product of this reaction (Scheme 14). 

Asymmetric selenoxide elimination of the optically active vinyl selenoxides affords optically active allenes and cyclohexylidenes. On the other hand, asymmetric [2,3]sigmatropic rearrangement of allylic selenoxides, selenimides, and selenium ylides leads to the formation of the corresponding optically active allylic alcohols, amines, and homoallylic selenides, respectively. 

Allyldimethyl- and allylmethylphenyl-selenonium salts react under similar conditions with potassium r-butoxide (THF, 20 "C, 20 h) and lead to homoallyl selenides in very high yields, including the particularly strained alkylidenecyclopropane derivatives (Scheme 65, b). These result from the metallation of... 

Homoallyl selenides are valuable precursors of dienes and allylidenecyclopropanes (Scheme 63). The dienes have been produced using the same sequence of reactions outlined above (Schemes 63 and 64), which involves the alkylation of the homoallyl selenide followed by treatment of the resulting salt with Bu OK in DMSO (Scheme 63). 

These reactions, coupl with the alkylations of sulfides and selenides, allow the homologation of primary alkyl halides - - - and the transformation of allyl halides to homoallyl halides. A related process, employing 2-methylthio- and 2-allylthio-thiazoline, allows the iodomeAylation (ICH2—) and the iodopropenylation (ICH2CH=CH—) of alkyl halides (Scheme 54).i3iii,i32.i7i... 

Allylytterbium bromide has also been reported to react with diselenides, aldehydes, and ketones to afford allyl selenides and homoallylic alcohols, respectively, in good yields under neutral and mild conditions (Scheme 304).1092... 

Allylation of a-thio-35), a-seleno-35) and a-silyl- 35,77) cyclopropyllithiums was not very successful35) but addition at —78 °C of 0.5 equivalent of copper (I) iodide-dimethylsulfide complex 35,106, W7> prior to the allylhalide leads 35,106,107) to a very high yield of homoallyl cyclopropyl sulfides or selenides (Scheme 24). Similar observations have been made on cyclobutyl derivatives3S). It is not clear at present whether a cuprate is involved in the process but we have evidence ( Se-NMR) that a new species is transiently being formed, at least in the seleno series. The synthesis of homoallyl cyclopropylsilanes was also reported 78) and involves the allylation of a postulated cuprate formed by the addition of lithium dibutyl cuprate to a-lithiocyclopropylsilane (Scheme 26). 

Homoallyl selenides. Selenoacetals are converted to homoallyl selenides in a Lewis acid-promoted reaction. 

In numerous synthetic studies it has been demonstrated that DMP can be used for a selective oxidation of alcohols containing sensitive functional groups, such as unsaturated alcohols [297,1215-1218], carbohydrates and polyhydroxy derivatives [1216, 1219-1221], silyl ethers [1222,1223], amines and amides [1224-1227], various nucleoside derivatives [1228-1231], selenides [1232], tellurides [1233], phosphine oxides [1234], homoallylic and homopropargylic alcohols [1235], fluoroalcohols [1236-1239] and boronate esters [1240]. Several representative examples of these oxidations are shown below in Schemes 3.349-3.354. Specifically, the functionalized allylic alcohols 870, the Baylis-Hillman adducts of aryl aldehydes and alkyl acrylates, are efficiently oxidized with DMP to the corresponding a-methylene-p-keto esters 871 (Scheme 3.349) [1217]. The attempted Swern oxidation of the same adducts 870 resulted in substitution of the allylic hydroxyl group by chloride. 

Several methods for the reduction of allylic functional groups have been reported. Although some of these are derivative of earlier procedures, useful improvements and modifications are noteworthy. For example, combination of [Pd(PhaP)4] with lithium triethylborohydride provides an effective system for the reductive removal of allylic ethers, sulphides, sulphones, selenides, and t-butyl-dimethylsilyl ethers. Many of these functional groups, of course, are not readily removed by other methods. Furthermore, this combination gives good to excellent maintenance of the regio- and stereo-integrity of the allylic double bonds. In a similar fashion, 2-tosyl homoallyl alcohols can be easily desulphonylated to... 

A further application of Ca-chiral aryl selenides derived from D-mannitol has appeared this year [see Vol 28, p.375]. Reagent 389 (from 388) promotes enantioselective selenoetherifications and selenolactonizations. Homoallylic alcohols 390 and 391 are converted to cyclic ethers 392 and 393 with >98% and 94% d.e., while p,y-unsaturated acids 394 and 395 formed lactones 396 and 397 in >98% and 92% d.e., respectively. 

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