An Unexpected (3→2)‐Hydride Shift in Phyllocladane (=13β‐Kaurane) Diterpenoids and in Related Trimethyl‐Substituted Bi‐ and Tricyclic Compounds

Abstract

The conversion of 2a,3a-dioxy-substituted phyllocladane derivatives into the corresponding 3-ketone proceeds in an unexpected manner: Depending on the reaction conditions, the corresponding 3b-hydroxysubstituted compound is formed almost quantitatively, or the desired ketone can be isolated directly (see preceding paper). The reaction mechanism is now disclosed to be a stereospecific C(3) 3 C(2)-hydride shift by investigating the reactions of the synthesized (AE)-trans-decalin-type (trans-1,5,5-trimethylbicyclo[4.4.0]decanes) and (AE)-podocarpane-type (trans-1,2,3,4,4a,9,10,10a-octahydro-1,1,4a-trimethylphenanthrenes) model compounds 25 and 35 and of their D-labeled isomers 25' and 35' (Scheme 6). The latter afforded the corresponding 3b-hydroxy (2b-D)-derivatives 38 and 39 as well as the (2b-D)-3-ketones of the general type 5b' (e.g., 36'), thus evidencing a suprafacial (C3) 3 C(2)-deuteride shift. This reaction mechanism seems to be a general feature of such 3a,4a-dioxy-substituted 1,5,5-trimethylbicyclo[4.4.0]decane congeners.

Oridonin Ring A-Based Diverse Constructions of Enone Functionality: Identification of Novel Dienone Analogues Effective for Highly Aggressive Breast Cancer by Inducing Apoptosis

“…The synthesis of analogues 19 and 20 started with the protection of the 7,14-dihydroxyl group of 1 as an acetonide. The 1-hydroxyl group of the acetonide was then selectively activated as a mesylate 16 , which further underwent an elimination reaction 31 in the presence of Li 2 CO 3 at 110 °C to provide the 1-ene analogue 17 in 84% yield. 10b To introduce a hydroxyl group to the 3-position of the A-ring, we initiated a key allylic oxidation by the treatment of 17 with selenium dioxide 32 in refluxing 1,4-dioxane to stereoselectively produce the 1-ene-3 β -hydroxyl analogue 18 in an excellent yield; 10b however, prolonged reaction time failed to give the enone product 19 .…”