Enantioselective Synthesis of Siloxyallenes from Alkynoylsilanes by Reduction and a Brook Rearrangement and Their Subsequent Trapping in a [4+2] Cycloaddition

Two flavors of selectivity: An enantioselective Meerwein–Ponndorf–Verley-type reduction of alkynoylsilanes by a chiral lithium amide followed by a Brook rearrangement and SE2′ electrophilic substitution provides the title compounds in a one-pot process. In the case of enynoylsilanes, the generated vinylallenes undergo in situ [4+2] cycloaddition to afford highly functionalized polycyclic compounds with unusual facial selectivity.