Alkylidenemalonic acid derivatives

Under various reaction conditions, dialkylsulfur diimides 1 react with alkylidenemalonic acid derivatives 2 to furnish the 1 /4,2,6-thiadiazines 3a-k or 5a, b.2s The cleavage of the substituent R2 from the 126,2,6-thiadiazines of type 4 required for the preparation of3a-k or 5a, b is only successful when R2 is a benzyl group. This debenzylation is catalyzed by acids. 

Melhod A The sulfur diimide 1 (5 mmol) and the alkylidenemalonic acid derivative 2 (5 mmol) were finely ground together and warmed to 60 °C for 4-48 h. The products were isolated and purified by column chromatography (silica gel, CHCl3/EtOAc 1 1) and subsequent recrystallization from MeCN/Et20. Method B Compound 4 (3 mmol) in EtOH (50 mL) was heated under reflux in the presence of /j-toluene-sulfonic acid (20 mg) for 72 h. The product was filtered under suction and dried in vacuo. 

Isopropylidene alkylidenemalonates undergo copper-catalysed conjugate addition with Grignard reagents yields of between 80 and 86% are reported for seven examples. Direct lithiation of the acrylic acid derivative (10), followed by reaction with COg, gives the oxaloacetic acid monoester (11) (Scheme 8). ... 

Bernadi and Scolastico, and later Evans in a more effective manner, indicated that the enantioselective addition reaction using silyl enol ethers can be catalyzed by Lewis acidic copper(II) cation complexes derived from bisoxazolines [38-40]. In the presence of the copper complex (S,S)-14 (10 mol %), silyl enol ethers derived from thioesters add to alkylidenemalonates or 2-alkenoyloxazo-lidone in high ees (Scheme 12). Bernadi, Scolastico, and Seebach employed a titanium complex derived from TADDOL for the addition of silyl enol ethers to nitroalkenes or 2-cyclopentenone [41-43], although these are stoichiometric reactions. 

The Lewis acid-promoted reactions of acrylates and propiolates with allylsilanes usually afford [2-1-2] adducts as described in the next section [470-473]. The corresponding [3-1-2] adducts are obtained as minor products although there are a few exceptions. The ratio of the two kinds of cycloadduct depends on the reaction temperature [470] - the proportion of [3-1-2] adducts increases with increasing temperature. The product ratio from cycloaddition to alkylidenemalonates and their derivatives is markedly temperature-dependent (Scheme 10.170) [474, 475]. Cyclobutanes are major products at low temperature, and [3-1-2] cycloaddition proceeds predominantly at higher temperature. In addition, the [2-1-2] cycloadducts are smoothly isomerized to the [3-1-2] adducts in the presence of a Lewis acid. This behavior clearly shows that [3-1-2] cycloaddition is thermodynamically favored. 

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