Thioketene hydrolysis

In contrast to titanium(IV) tetrachloride, which causes polymerization of a,3-unsaturated esters, aluminum triflate88 or aluminum-impregnated montmorillonite87b are excellent promoters of silyl ketene acetal additions to a,(3-unsaturated esters (Scheme 35). Similarly, the addition of silyl ketene acetals and enol silyl ethers to nitroalkenes, followed by Nef-type work-up, affords y-keto esters (216) and y-di-ketones (218), respectively (Scheme 35).89a>89b Mechanistically, the y-diketones (218) arise from Nef-type hydrolysis of an initial nitronate ester (217).89e 89d Mukaiyama reports that SbCls-Sn(OTf)2 catalyzes diastereoselective anti additions of silyl ketene acetals, silyl thioketene acetals and enol silyl ethers to a,(3-unsaturated thioesters (219).90... 

A recent notable finding in this field is Mukaiyama aldol reactions in aqueous medium (THF H20 = 9 1) catalyzed by metal salts. Lewis acids based on Fe(II), Cu(II), and Zn(II), and those of some main group metals and lanthanides are stable in water. Remarkably, the aldol reaction shown in Sch. 29 occurs more rapidly than the hydrolysis of the silyl enol ether [137]. In the presence of surfactants (dodecyl sulfates or dodecane sulfonate salts), reactions of thioketene silyl acetals with benzaldehyde can be performed in water [138]. 

The diazomethane-keten reaction gave no 1,3-dipolar adducts, such as those obtained readily enough from the corresponding thioketen (see Vol. 1, p. 44), even at low temperatures. The 2 1 adduct obtained (165) cannot arise by prior dimerization of the keten, whose jS-lactone dimer (166) reacts to give a y-lactone (167) by methylene insertion at the C—O bond, so that quite different hydrolysis products are obtained (see Scheme 48). ... 

The reaction of thioketens and amino-azirines proceeds by C=N cleavage to give the dipolar species (293) or ketenimines (294), depending upon substitution hydrolysis of the latter leads to 2-thiazolin-5-ones (295). There are few general routes to 1,3,4-thiadiazolines and a new method, discovered accidentally, provides the derivatives (296) which, since they have amidine characteristics, will probably prove to be useful synthons. Thiadiazolidine diones are readily available from metallated iV-(trimethylsilyl) alkylamines. 

One Carbon Homologation of Aldehydes via a Peterson Olefination. 2-Trimethylsilyl-l,3-dithianes have been widely used in the formation of thioketene acetals. This reaction is the first of a two-step procedure that results in the one carbon homologation of an aldehyde or ketone via a 2-lithio-2-TMS-1,3-dithiane-mediated Peterson olefination, followed by hydrolysis of the dithiane to give the corresponding ester (eq 20). ... 

In the [2+2] cycloaddition reaction of thioketenes with chloro- and fluorosulfonyl isocyanates the [2+2] cycloadducts are not isolated, but j8-thiolactams resulting from the hydrolysis of the halosulfonyl groups are obtained. 

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