Sulfides, 1-alkynyl metallation

S -Analogues of lithium or sodium ynolates (thioalkynolates or alkynethiolates) are prepared from lithium or sodium acetylide and sulfur, and are trapped as alkynyl sulfides with bromoethane (equation 77). In a synthetic approach analogous to equation 72, 5-lithio-l,2,3-thiadiazoles (198) also afford lithium alkynethiolates (199) by elimination of nitrogen (equation 78) . Alkynyl sulfides (200) are treated with lithium in ammonia to afford lithium alkynylthiolates (199) (equation 79) °. Theoretical studies on the structure of alkali metal alkynylthiolates are reported. ... 

Metallation of various 1-alkynyl sulfides, followed by alkylation of the resulting anion leads exclusively to a-alkylated allenyl sulfides (Scheme 39). 

A small number of enantiomerically pure Lewis acid catalysts have been investigated in an effort to develop a catalytic asymmetric process. Initial work in this area was carried out by Narasaka and coworkers using the titanium complex derived from diol (8.216) in the cycloaddition of electron-deficient oxazolidinones such as (8.217) with ketene dithioacetal (8.218), alkenyl sulfides and alkynyl sulfides. Cyclic alkenes can be used in this reaction and up to 73% ee has been obtained in the [2- -2] cycloaddition ofthioacetylene (8.220) and derivatives with2-methoxycarbonyl-2-cyclopenten-l-one (8.221) usingthe copper catalyst generated with bis-pyridine (8.222). Furthermore, up to 99% ee has been obtained in the [2-1-2] cycloaddition of norbornene with alkynyl esters using rhodium/Hs-BINAP catalysts. This reaction is not restricted to the use of transition metal-based Lewis... 

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