Alkynyl silicon compound

Another example of boration of Me2Si(C CMe)2 150 was reported by Wrackmeyer et al. <2001CEJ775>. 1-Boraadamantane 153 reacted with di(l-alkynyl)silicon compound 150 in a 1 1 ratio by intermolecular 1,1-alkylbora-tion. This led to the novel octacyclic 7-metalla-2,5-diboranorbornane derivative 7 (Equation 26 Scheme 1). 

Jesi and /csn couphngs have been used by Wrackmeyer et a/. in order to follow the reaction between 1-boraadamantane and di(l-alkynyl)silicon and -tin compounds of the type (Me2M(C = C)R)2, M = Si or Sn, and to characterise some novel 7-metalla-2,5-diboranorbornane derivatives obtained as products. 

Alkynyl(diisopropylsilyl)oxy-diazoacetates (295) undergo intramolecular 1,3-dipolar cycloaddition in good yield when R1 = H (isolation of silver pyrazolide 296 was possible) and R2,R2 = Me,Me or (CH2)5, but no reaction occurred when R = H, R2 = H or R1 = Me (340). The silicon substitution is apparently crucial. Replacement of the Si(i-Pr)2 in 295 (R1 = R2 = H) by Si(f-Bu)2 allowed an uncatalyzed intramolecular [3 + 2] cycloaddition to take place [xylene, 140-160°C, 11% yield (340)], while Ag(I) catalysis led to decomposition. A diazoacetic acid (2-propyn-l-yl)oxysilyl ester also produced a bicyclic pyrazole, but in low yield. On the other hand, the same diazo compound 295, which reacted intra-molecularly under silver ion catalysis, underwent dimerization by an mfermolecular... 

However, if it is not advisable to react the central silicon atom, some other group needs to be introduced that can be further functionalized. This can be an alkynyl group, for example. To test the compatibility of these groups with the formation of silylanions, a number of model compounds were prepared and subjected to metalation with potassium fert-butoxide (Eq. 9). The results were surprising in that the reactions with the alkoxide proceeded substantially faster than in the previously described examples, with the phenylethynyl derivative being completely consumed almost instantaneously after mixing of reagents and addition of the solvent. Reaction of potassium fert-butoxide with (MesSijsSi-C CH showed that deprotonation of the alkynyl substituent by the alkoxide is not a competitive reaction. 

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