Metal-free Hydroalkoxylation-Formal [4+2] Cycloaddition Cascade for the Synthesis of Ketals
作者:Santosh J. Gharpure、Santosh K. Nanda、Padmaja、Yogesh G. Shelke
DOI:10.1002/chem.201701659
日期:2017.7.26
A transition metalfree, acid promoted cascade hydroalkoxylation–formal [4+2] cycloaddition of various alkynols with salicylaldehyde is demonstrated for the synthesis of tetrahydrofurano/pyrano‐chromenes and spiroketals. In general, alkynols underwent hydroalkoxylations in an endo‐dig manner when internal alkynes were used to furnish the heteroannular ketals, whereas terminal alkynes proceeded in an
Synthesis of spiroacetals using functionalised titanium carbenoids
作者:Calver A. Main、Shahzad S. Rahman、Richard C. Hartley
DOI:10.1016/j.tetlet.2008.05.094
日期:2008.8
titanium carbenoid reagents (Schrock carbenes) followed by acid-induced cyclisation of the resulting enol ethers constitutes a new method for the preparation of [4.4], [4.5] and [5.5] spiroacetals (1,6-dioxaspiro[4.4]nonanes, 1,6-dioxaspiro[4.5]decanes and 1,7-dioxaspiro[5.5]undecanes, respectively, sometimes termed 5,5-, 5,6- and 6,6-spiroketals). The titanium carbenoids are easily generated from readily