Thioketenes amines

The enantioselectivity of Sn(II) enolate reactions can be controlled by chiral diamine additives. These reagents are particularly effective for silyl thioketene acetals.162 Several diamines derived from proline have been explored and l-methyl-2-(l-piperidinomethyl)pyrrolidine 21 is an example. Even higher enantioselectivity can be achieved by attachment of bicyclic amines to the pyrrolidinomethyl group.163... 

The reaction of thioketenes, generated by flash-vacuum pyrolysis (Section IU.C.l.b), with secondary amines affords the corresponding thioamides and is the standard trapping procedure for these unstable compounds288 (equation 114). 

The rearrangement that occurs when thioethers of type 347 are heated in the presence of secondary amines provides an interesting analogy to 1,5-diynes . The products are 349, 350 and 351, and it is postulated that these arise by the reaction of the amine with the thioketene 348, which, in turn, is formed by a [3, 3] sigmatropic rearrangement of 347... 

The 4-methylene-l,3-dithietane-2-ones lose carbon oxysulfide to give thio-ketenes that dimerize to 2,4-dimethylene-l,3-dithietanes, as exemplified by the flash-vacuum thermolysis of 551. Reaction of several methylene 1,3-dithietane-2-ones with secondary amines also appears to proceed via loss of carbon oxysulfide followed by addition of the amine to the thioketene. An exception to the loss of carbon oxysulfide is the reaction of a guanidine derivative with 551 to give the ring-opened product 552. ... 

Thioketenes (34) are highly electrophilic and give a smooth reaction with ammonia or amines. In fact, addition of a secondary amine offers the best way to scavenge a suspected thioketene. But the approach also deserves interest from the point of view of thioamide synthesis as it allows very mild and nonreducing conditions, tolerating the presence of sensitive additional functional groups such as cyano, nitro, or sulfonyl residues (equation... 

In the reaction of alkynyl thiolates (39) with excess diethylamine, the amine provides the proton to generate an aldothioketene (40) and, at the same time, serves as the trapping reagent (Scheme 9). Bis(trimethylsilyl)thioketene (41) gives a smooth reaction with amines, but one silyl group is always displaced in the process yielding thioamides (42 equation 17). ... 

Alknyl silyl sulfides, R C=CSSiR 3, which are readily obtained by silylation of anions (39), react as thioketene equivalents. Thus, (3-thiolactams are formed in the reaction with C=N systems (c/. Volume 5, (Chapter 2.2) and thioamides on addition of amines equation (18) shows a typical example. This approach has great promise for the thioacylation of very sensitive natural products. 

The azo-compound (248) rearranges thermally to the pyrazole (249). The 1-pyrazoline (250) is formed from the thioketen 5-oxide Bu Pr C=C=SO and 2-diazopropane.The allyl chloride H2C=C(COPh)CH2Cl reacts with 1,1-dimethylhydrazine to yield the pyrazolidine derivative (251). Numerous betaines (252 R, R, R = H or Me) have been prepared by the action of aromatic aldehydes on the appropriate pyrazolidinones. Treatment of diethyl acetylmalonate with 1,1-dimethylhydrazine affords the amine-imide (253). ... 

Schaumann and his group [88-91] disclosed that thioketenes are efficiently produced by rearrangement of (silylethynyl) vinyl sulfides (R = SiMe,) under mild conditions (Scheme9.15). The products can be trapped by amines, providing y-un-saturated thioamides. In the absence of the silyl group, thioketenes could not be isolated, but were converted in thioamides by reaction with amines [92]. 

A further extensive paper and two associated patents have revealed more of the interesting chemistry of bis(trifluoromethyl)thioketen. The reactions encompassed by these publications include additions of water, alcohols, thiols, hydrogen bromide, primary and secondary amines, NN-dimethylanilines, ethers, and silicon and tin hydrides (Scheme 30), as well as an extensive series of ene reactions (Scheme 31). 

Various ring-opened products are obtained from desaurins and nucleophiles (amines, mercaptides, hydrazine). Several thioketens are formed in the loss of carbonyl sulphide from 4-dialkylidene-l,3-dithietan-2-ones. ... 

Raasch has extended his studies of the reactivity of bis(trifluoro-methyl)thioketen (141). Scheme 8 gives a survey of the reactions that have been carried out. Thus common nucleophilic agents such as alcohols, thiols, primary, and secondary amines, etc., react with (141) with conservation of the C=S double bond, whereas the C==C double bond remains in the products of the reactions of (141) with certain ethers, dimethylaniline, and hydrides of tin and silicon. Compound (141) reacted with a variety of olehnic substances in accordance with the general ene-reaction formalism, yielding allyl vinyl sulphides (148). The formation... 

A variety of thioamides and heterocyclic compounds containing the thiolactam grouping have been synthesized by thioacylation of amines by means of thioketens, thioacyl chlorides,ethyl thionoformate, dithio-acids 3, l(4H)-benzothiazine-4-thiones, 2,4-dithioxodihydro-... 

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