The aldol-type condensation of methyl diazoacetate with 3-organyl-silyl and -germyl propynals and their carbon analogues

The optimal conditions for the uncatalyzed, selective addition of methyl diazoacetate (I) to the carbonyl group of the substituted propyn-1-als RCCCHO (II) (R = alkyl, Alk₃Si, Et₃Ge) to give the corresponding methyl esters of 2-diazo-3-hydroxy-4-pentyn carboxylic acid RCCCH(OH)C(N₂)COOMe (III) have been found. Shielding of the triple bond in II by the bulky R group or complexation with dicobalt octacarbonyl, the presence of strong electron acceptor (4-NO₂C₆H₄) in the 3-position of II, and the low polarity of the solvent result in the selective aldol type condensation. The reaction of γ-hydroxy-propynals R¹R²C(OH)CCHO with methyl diazoacetate also proceeds by the aldol-type addition and involves two molecules of the propynal with the formation of diacetylenic diazotetraoles {A figure is presented} (VIII). The β-addition of methyl diazoacetate to the triple bond in trialkylsilyl or -germyl propynals leads to the isomeric formyl pyrazoles, IV and V. The presence of the Si- or Ge-containing substituents in the 4-position of IV promotes their dimerization into the tricyclic hemiaminals, VI.