Palladium‐Catalyzed Allylic Substitution for the Synthesis of Pericosines

Abstract

As equence of vinylalumination of a-substituted aldehydes,r ing-closingm etathesis (RCM), and palladium-catalyzed allylic substitution was utilized to prepare the biologically active natural products, pericosines, from d-ribose. The anti-adduct of vinylaluminationw as transformed into pericosine Aa fter RCM, removalo ft he 4-methoxybenzyl protect-ing group, and chlorination. The diacetate of the anti-adduct was converted to pericosine Ca fter the palladium-catalyzed, S N 2'-type, allylic substitution. However,a nu nexpected dimeric product was generated in utilizing this approacht o preparep ericosine E. Results and DiscussionRetrosynthetic analysis of the pericosines is shown in Scheme1,w hich indicates that cyclitol 1 is the key intermediate. Furtherm anipulations to the allylic alcohol, such as S N 2, S N 2',o rp alladium-catalyzeds ubstitution reactions, could lead to the target pericosines A, C, andE .C yclitol 1 could be obtained from the RCM reaction of the 1,7-diene 3,d erived from Figure 1. Structure of naturallyo ccurring pericosines.

A Synthetic Approach to Several C7-Carbasugars via a Key Intramolecular Morita–Baylis–Hillman Reaction

“…Due to their structural diversity and promising biological activities, the natural C7-cyclitols have attracted great synthetic interest. ,, The crucial step in many syntheses is the closure of the polyhydroxylated six-membered carbon rings from various precursors via some conceptually different reactions. Besides the most widely used ring closing metathesis (RCM reaction), aldol condensation, Horner–Wadsworth–Emmons (HWE) reaction, Ferrier carbocyclization, 1,3-dipolar cycloaddition, Diels–Alder reaction, Nozaki–Hiyama–Kishi (NHK) reaction, seleno-Michael/aldol reaction, and gold-catalyzed 1,6-diynes cyclization have also been proven as feasible methods to achieve cyclization of some appropriate precursors in the synthesis of the natural C7-carbasugars. However, Morita–Baylis–Hillman reaction is not employed to construct the hydroxylated cyclohexenyl rings of the C7-carbasugars yet.…”