Silicon-tethered 1,3-dipolar cycloaddition reactions of unsaturated alpha-silyl-alpha-diazoacetates and diazoacetic acid silyl esters

Methyl alpha-[di-tert-butyl(propargyloxy)silyl]-alpha-diazoacetate (6) unde rgoes a thermal intramolecular 1,3-dipolar cycloaddition reaction to form b icyclic pyrazole 8. Structurally similar, but Si-iPr(2)- rather than Si-tBu (2)-linked diazoacetates 12a,b, which react thermally to form cyclooligomer s by inter-/intramolecular cycloaddition sequences, undergo the intramolecu lar [3+2] cycloaddition in the presence of silver(I) oxide. Silver pyrazoli de 13a could be isolated and was transformed into NH-pyrazole 14a under aci dic conditions. (Alkenyloxy)silyl and (alkynyloxy)silyl diazoacetates 15a-h were prepared from a silyl bis(triflate), tert-butyl diazoacetate, and an unsaturated alcohol. A thermally induced intramolecular [3+2] cycloaddition leading to bicyclic pyrazoles 16 was observed for 15b and 15c, while all o ther diazoacetates 15 underwent unspecific decomposition. Only in the case of 15f, the tetracyclic 1,5-diazabicyclo[3.3.0]octane derivative 20 could b e isolated in 2% yield and was structurally characterized by X-ray diffract ion analysis. (C) 2000 Published by Elsevier Science Ltd.