Highly Regio- and Stereoselective Intramolecular Rearrangement of Glycidol Acetal to Alkoxy Cyclic Acetals

Abstract

A new class of highly regio-and stereoselective intramolecular rearrangements of glycidol acetals to produce alkoxylated 1,3-dioxolane/1,3-dioxane is demonstrated. Selective Lewis acid activation of acetal generates an oxocarbenium ion that initiates the epoxide ring-opening event, giving the bicyclic [3,1,0]epoxonium ion intermediate that undergoes exo/endo-selective opening by a tethered alkoxide. Mechanistic insights into preferential acetal activation over the epoxide were obtained by crossover experiments. The method was applied in the total synthesis of parvistone B and its 8-ethoxy analogue.

Effective In Situ Alkoxide Trapping by TMSX in the Presence of TPP Catalyst in Glycidol Acetal Rearrangements

“…The allyl alcohol 15 underwent Sharpless asymmetric epoxidation to yield glycidol 16 , which was subsequently treated with ethyl vinyl ether to produce glycidol acetal 17 . However, when reacted with BF 3 ·OEt 2 , glycidol acetal 17 exclusively produced 1,3-dioxolane 17b . The yield was 88%, with no fully ( 17a ) or partially cyclized products.…”

“…This silyl-initiated glycidol acetal rearrangement reaction follows a nonstereoselective S N 1-type epoxide opening mechanism. However, the reaction is highly endo -selective, similar to simple Lewis acid-catalyzed glycidol acetal rearrangement …”

A Biomimetic Stereoselective Approach to Euolutchuol C and Its Structural Assignment

“…Upon examining all the structural features, we have concluded that the only way to figure out the exact stereochemistry of euolutchuol C is to synthesize its four possible stereoisomers 1 a – d . We have initiated the synthesis of these diterpenoid molecules as part of our ongoing projects on the total synthesis of terpenoid molecules [5] . Given thier intricate architectures and notable biological and pharmacological features, euolutchuols serve as appealing synthetic targets.…”

“…Furthermore, in cases where the decalin system has an abietane configuration, the C-15 stereogenic center generates two diastereomers 1 a and 1 b, whereas the ent-abietane system produces isomers 1 c and 1 d. Upon examining all the structural features, we have concluded that the only way to figure out the exact stereochemistry of euolutchuol C is to synthesize its four possible stereoisomers 1 a-d. We have initiated the synthesis of these diterpenoid molecules as part of our ongoing projects on the total synthesis of terpenoid molecules. [5] Given thier intricate architectures and notable biological and pharmacological features, euolutchuols serve as appealing synthetic targets. To the best of our knowledge, no total or partial synthesis of these compounds has ever been documented.…”

Diarylborinic Acid-Catalyzed Ring Opening of cis-4-Hydroxymethyl-1,2-Cyclopentene Oxides: Synthesis of 1,2,4-Trisubstituted Cyclopentanes

“…For ring-opening reactions of epoxides, metal Lewis acid catalysts or small organic molecule catalysts are well-developed, and excellent results have been achieved . Organoboron compounds, as another type of Lewis acid, have also been exploited and applied for this reaction, delivering different regioselective products. In 2003, trialkyl-borates-mediated ring-opening reactions of 2,3-epoxy alcohols have been exploited by Miyashita and co-workers, delivering the C2-selective products through endomode epoxide opening of intramolecular boron chelation (Scheme a) .…”