Intramolecular aldol cyclization of -lyxo-Hexos-5-ulose derivatives: A new diastereoselective synthesis of -chiro-Inositol

The DBU-promoted intramolecular aldol condensation of two partially protected -lyxo-hexos-5-ulose derivatives (8 and 9), in turn obtained starting from methyl β- -galactopyranoside, takes place with fairly good yield and complete diastereoselectivity to give 2 -(2,3,6/4,5)-pentahydroxycyclohexanone derivatives, 10 and 11. The stereoselective reduction of inosose 10 with sodium triacetoxyborohydride leads, after catalytic debenzylation, to -chiro-inositol (1), while the sodium borohydride reduction furnishes, with opposite stereoselectivity, a derivative of allo-inositol.