1-Iodo-1-selenoalkenes as versatile alkene 1,1-dianion equivalents. Novel connective approach towards the tetrahydropyran subunit of polycavernoside A

syn-Hydroalumination of 2,4,6-triisopropylphenylselanyl-1-alkynes with DIBAL-H followed by Al/I exchange with I2 afforded exclusively (E)-1-iodo-1-selenoalkenes in good yields. 1-Iodo-1-selenopropene proved to be a convenient 1,1 dianion equivalent, leading to the stereodivergent synthesis of allylsilanes and . Adduct , an intermediate in the synthesis of the tetrahydropyran subunit of polycavernoside A, was efficiently synthesised from allylsilane and aldehyde via an intramolecular Sakurai cyclisation.