Allenyl thioethers

The inverse isomerization mode, providing allenyl thioethers from alkynyl thioethers, is also known [309, 310] for example, 124 is first deprotonated with n-butyllithium and then protonated with ammonium chloride [311] (Scheme 1.55). 

Sulfur-containing allenes can be subdivided into donor-functionalized allenes such as allenyl thioethers and into acceptor-functionalized allenes such as allenyl sulfoxides and sulfones. In this section only the synthesis and chemistry of donor-substituted sulfur-containing allenes will be summarized. 

An interesting approach to allenyl thioethers has been reported by Huang and Xiong, which is based on a novel three-component reaction. Treatment of 1-alkynyl-phosphine oxides 310 with lithium alkylthiolates 311 in the presence of an aldehyde 312 provides the expected highly substituted allenyl thioethers 313 in good yield (Scheme 8.84) [173]. Unfortunately, this procedure could not be extended to arylthio-lates. 

Very recently, Davies and coworkers have reported a silver-catalyzed Doyle-Kirmse reaction of ally lie and propargylic sulfides with ethyl diazophenylacetate (35). A selection of examples was investigated providing the rearranged products, either homoallylic thioethers (76 —> 77, Scheme 8.14a) or allenyl thioethers (78 —> 79, Scheme 8.14b) in good yields, and with good overall scope.40... 

Startg. allenyl thioether added during 5 min. with vigorous stirring to a soln. of KNH2 in liq. NHg, after 10 min. dry ether added, stirring continued 1 hr., NH3 evaporated on a water bath, and the residue treated with water 1,3-enyne. Y 82-88%. E. s. P. P. Montijn and L. Brandsma, R. 83, 456 (1964) 2-en-4-ynols s. R. 84, 560 (1965). 

Investigations by Vermeer and co-workers have shown that 3-substituted allenyl methyl thioethers 309 can be prepared by regioselective addition of an alkyl silver species to the terminal C=C bond of enyne sulfides 308 (Scheme 8.83) [172], Remarkably, this method can also be applied to the preparation of several allenyl-phosphines starting from the corresponding phosphorus-substituted alkynes. 

Cutting and Parsons described the transformation of acetylenic alcohols 314 into allenyl phenyl thioethers 316 by a two-step procedure (Scheme 8.85) [174], Deprotonation of alkynes 314 with n-butyllithium is followed by addition of phenylsulfenyl chloride, forming sulfenyloxy intermediates which subsequently rearrange to allenic sulfoxides 315. Treatment of allenes 315 with methyllithium results in loss of the sulfoxide moiety to form allenyl sulfides 316 in reasonable yields. 

Methyl allenyl sulfide (methylallenyl thioether) (20) Dipole moment 334,... 

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