Formal Synthesis of d-myo-Inositol 1,4,5-Tris(dihydrogen phosphate):  Cyclization by an Unusual Ene Reaction and Use of the Bu₂SnCl₂/Bu₂SnH₂ Reagent for Generating an Equatorial Alcohol

d-Glucose was converted into the propargyl silane aldehyde 5, which, on treatment with camphorsulfonic acid, cyclized with retention of silicon. The allenic product (7) was elaborated via ketone 24 into 4, which had previously been converted into d-myo-inositol 1,4,5-tris(dihydrogen phosphate). Selective reduction of the advanced intermediate 24 was accomplished with Bu₂SnCl₂/Bu₂SnH₂, a reagent mixture that shows a very strong preference for generating equatorial alcohols. The cyclization step leading to allene 7 was studied by examining a number of model compounds; the unusual retention of silicon appears to be limited to highly oxygenated substrates, such as 5 and its all-benzyl analogue (27).