3-Trimethylsilyl-2-propynoate

Diels-Alder reactions of 1,3-cyclohexadienes and 3-(trimethylsilyl)propynoates. A new synthesis of orf/7o-(trimethylsilyl)benzoate esters [149]... 

Ni(cod)2 (210 mg, 0.78 mmol) and tris(2-phenylphenyl) phosphite (420 mg, 0.78 mmol) were dissolved in toluene (10 mL). The solution was heated to 80 °C and at that temperature a mixture of (diphenylmethyl-ene)cyclopropane (6.70 g, 32.7 mmol) and methyl 3-(trimethylsilyl)propynoate (5.10 g, 32.7 mmol) was added dropwise within 30 min. After an additional 8 h at 80 C, the mixture was distilled to yield a forerun (25.07 g, mainly toluene) and then a colorless distillate (10.34 g bp 120-140 C/10 Torr) that solidihed upon standing at rt. The latter contained about 13% of unreacted (diphenylmethylene)cyclopropane (calculated conversion 80%) and 72% of the cycloadduct, as determined by GC analysis. Recrystallization (toluene) afforded the pure cycloadduct as colorless needles yield 7.44g (63%) mp 172°C. 

See also Tris(trimethylsilyl)silane Ethyl propynoate... 

Cycloadditions of cyclic ketene trimethylsilyl acetals with ethyl propynoate and other electrophilic alkines were run at room temperature, without a catalyst and solvent-free [47]. 

Another case where the formation of the phosphane arm is the result of a Cp methyl C.H activation process is the reaction of bis(trimethylsilyl)derivative 240, which is closely related to 232, with 2 equiv of methyl or ethyl propynoate. The two propynoate units are coupled, and the unusually complex structures 243 and 244 are formed (Scheme 45). 243 has been the subject of an X-ray crystallographic investigation. Although the authors do not specifically comment on the stereochemistry, the fact that both compounds show one singlet in the P NMR spectrum indicates that 243 and 244 are formed diaste-reoselectively, presumably via 241 and 242. 

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