Chemistry of Tonghaosu Analogs: Novel Acid‐Catalyzed Nucleophilic Addition to the Dienyl Acetal System

Abstract

The acid-catalyzed nucleophilic addition reaction of spiroketal enol ether-containing tonghaosu analogs 2 was explored. Soft nucleophiles, such as mercaptans, alcohols and heteroaromatic compounds, gave rise exclusively to 1,6-adducts, while harder nucleophiles, such as Grignard reagents, afforded mixtures of 1,2-and 1,6-adducts. The reaction with cysteine and glutathione, which might be related to the mode of action of insect antifeeding, also took place smoothly.

Reaction of Acetals with Various Carbon Nucleophiles under Non‐Acidic Conditions: CC Bond Formation via a Pyridinium‐Type Salt

“…[4] a,b-Unsaturated acetals could react with Grignard reagents alone or in the presence of a Lewis acid. [5] Organocuprates activated by BF 3 ·Et 2 O could also react with acetals [6] via oxonium ion intermediates.…”

“…On the other hand, the use of organometallic reagents as nucleophiles is not very common. Some acetals, such as a,b-unsaturated acetals, can react with these reagents to give substituted products [2][3][4][5] or the Lewis-acid-activated organocuprates can react with the acetals. [6] Therefore, nucleophiles for CÀC bond formations are rather limited.…”

Rapid and Stereoselective Synthesis of Spirocyclic Ethers via the Intramolecular Piancatelli Rearrangement

“…Wu et al have extensively studied the chemistry of spiroketal enol ether derivatives ( 8 ), but to our knowledge conditions that facilitate the formation of oxocarbenium ion A have never been reported. , Spiroketal enol ether derivatives are known to ring open in the opposite direction in the presence of an acid catalyst, forming oxocarbenium ion D (eq ). For example, in the presence of catalytic amounts of acid ( p -TsOH or ZnCl 2 ), alcohols react with 8 via D to give furan derivative 10 . Similar conditions, ZnCl 2 in aqueous 1,2-dimethoxyethane, are reported to convert 8 into oxabicyclic cyclopentenones ( 11 ) .…”

Catalytic Formal Benzylic C–H Bond Functionalization of 2,5-Dialkylfuran Derivatives with Ferrocenyl Alcohols as Alkylation Reagents

“…The tendency toward rearomatization of furan serves as the driving force for superafacial shift. 24 As far as 4 is concerned (Scheme 5, b), due to the higher steric hindrance of nonmethyl aliphatic groups, e.g., benzyl, 10 would be more readily attacked by the less steric demanding C5 of 4, followed by consecutive deprotonation and 1,5-sigmatropic alkyl shift to furnish 5, which can elegantly rationalize the regiospecificity of Scheme 3. Substrate Scope Investigation of 2,5-Dialkylfuran Derivatives a a Reaction conditions: 1a (0.1 mmol), 4 (0.3 mmol), and CSA (10 mol %) in 1 mL of DCE at room temperature, isolated yield.…”

“…After deprotonation of 11 , the dearomatized intermediate 12 is afforded, which subsequently undergoes a sigmatropic superafacial shift of ferrocenylmethyl to yield 3a . The tendency toward rearomatization of furan serves as the driving force for superafacial shift . As far as 4 is concerned (Scheme , b), due to the higher steric hindrance of nonmethyl aliphatic groups, e.g., benzyl, 10 would be more readily attacked by the less steric demanding C5 of 4 , followed by consecutive deprotonation and 1,5-sigmatropic alkyl shift to furnish 5 , which can elegantly rationalize the regiospecificity of benzylic C–H bond alkylation.…”