Synthesis of silyl, germyl, and phosphino-substituted acylketenes from pivaloylethoxyacetylene

The reaction of pivaloylethoxyacetylene with silicon halides, which has been found to occur as a 1,4‐addition, leads to allenic ethers, which readily eliminate ethyl halides and are converted to previously unknown types of ketenes—stable element‐substituted acylketenes. Germanium‐substituted acylketenes are also formed; however, clear evidence of 1,4‐addition of germanium halides was not obtained. In the reaction between Ph2PCl and pivaloylethoxyacetylene, phosphorus (III) substituted acylketenes initially formed underwent rapid [3 + 3] cyclodimerization.