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 (1H and 13C 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
螺
缩醛酮体系可以容易地通过将Norrish II型反应应用于在
乙缩醛氢的δ位具有羰基的
四氢吡喃酮缩醛得到。通过IR,NMR(1 H和13 C)建立的螺环和双螺环的结构显示出
四氢呋喃环的CO键的轴向构象。