Synthese photochimique et etude structurale d'alcoxy-spirocetals et de trioxa-bis-spirocetals

Abstract The spiroketal systems can be obtained easily by a Norrish type II reaction applied to tetrahydropyranic ketoacetals having a carbonyl group in δ position of the acetalic hydrogen. The structures of spirans and bispirans established by IR, NMR ( 1 H and 13 C show an axial conformation for the C-O bond of the tetrahydrofuran ring. With the bispirans this anomeric effect requires for some isomers a twist boat conformation of the tetrahydropyran ring.