Studies on the syntheses of heterocyclic compounds. 675. A facile regiospecific and stereocontrolled synthesis of a diterpene alkaloid intermediate from benzocyclobutenes
TL;DR: In this paper, the Jodid (III) (mittels ublicher Methoden aus α-Methylacetessigsauremethylester erhaltlich) zu dem Kondensationsprodukt (IV), das bei Thermolyse regiospezifisch und stereoselektiv in das Octalin (V) ubergeht.
Abstract: Das aus der Cyanpropionsaure (I) erhaltliche Benzocyclobuten (II) reagiert mit dem Jodid (III) (mittels ublicher Methoden aus α-Methylacetessigsauremethylester erhaltlich) zu dem Kondensationsprodukt (IV), das bei Thermolyse regiospezifisch und stereoselektiv in das Octalin (V) ubergeht.
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TL;DR: All reports of total syntheses that utilize arynes in ways that build complexity or introduce motifs essential to the completion of their targets are recounted.
Abstract: Within 14 years of the seminal experiments of J. D. Roberts
leading to the first proposal of the structure of benzyne (1), synthetic organic chemists recognized the potential to exploit this highly reactive intermediate (and its substituted variants) in the total synthesis of natural products. More specifically, it was recognized that arynes offered the strategic advantage of rapidly functionalizing an aromatic ring by forming multiple carbon− carbon or carbon−heteroatom bonds in a single operation, often in a regioselective manner. Initially, the scope of synthetic
applications was somewhat limited by the harsh conditions
required to produce the aryne species. Many of these methods required strong bases, such as n-BuLi, or high temperatures (Scheme 1). However, with the development of milder methods for the generation of arynes came increased interest in employing them in the synthesis of more complex polycyclic systems. Most recently, the use of o-silyl aryl triflates as aryne precursors has allowed generation of the reactive intermediate under almost neutral conditions.
To date, over 75 individual natural products have been
prepared using arynes to generate key synthetic intermediates. Herein are recounted the reports of total syntheses that utilize arynes in ways that build complexity or introduce motifs essential to the completion of their targets. The methods by which the authors featured in this review accomplish this task reflect the versatility of arynes as reactive intermediates for synthesis (Scheme 2). For the purposes of organization, the syntheses are divided into subgroups on the basis of the type of aryne transformation: (i) nucleophilic additions or multicomponent reactions, (ii) σ-bond insertion reactions, (iii) [4 + 2]- and [2 + 2]-cycloaddition strategies, and (iv) metal-catalyzed aryne reactions.
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TL;DR: In this article, the reactions of nitrile-stabilized anions are grouped according to the nature of the substituents attached to the carbanion center bearing the n-group, including alkyl, alkenyl, alkynyl, and aryl groups.
Abstract: The utilization of carbanions stabilized by various electron-withdrawing groups to effect carboncarbon bond formation occupies a central position in organic synthesis. This chapter focuses on the reactions of nitrile-stabilized carbanions with an array of carbon electrophiles and updates another chapter along these lines in this series. Subsequent review articles have dealt with various aspects of the chemistry of nitrile-stabilized carbanions. In this review, the reactions of nitrile-stabilized anions are grouped according to the nature of the substituents attached to the carbanion center bearing the nitrile group. These substituents include alkyl, alkenyl, alkynyl, and aryl groups as well as various α-oriented halogen-, oxygen-, nitrogen-, sulfur-, and selenium-containing groups. Notably absent from this survey are the carbanions derived from active methylene compounds bearing two electron-withdrawing groups such as cyanoacetate esters, malononitriles, α-sulfonylnitriles, and α-phosphorylnitriles. Also absent are those carbanions such as Reissert compounds, which are the subject of comprehensive reviews.
The chapter is arbitrarily subdivided into six sections: (1) reactions of alkyl-, aryl-, and heteroaryl-substituted nitriles; (2) reactions of α,β- and β,γ-unsaturated nitriles as well as tolunitriles; (3) reactions of cyanohydrins and their hydroxyl-protected derivatives; (4) reactions of nitriles bearing α-sulfur and α-selenium substituents; (5) reactions of α-(dialkylamino)nitriles; and (6) reactions of α-halonitriles. Within each of these sections, the reactions are further subdivided according to the nature of the electrophile: (1) alkylation reactions employing alkyl halides, alkyl sulfonates, dialkyl sulfates, and epoxides; (2) arylation reactions involving the substitution of hydrogen, halogen, nitro, or alkoxy groups on aryl or heteroaryl substrates; (3) acylation reactions employing carboxylic esters, anhydrides, acid chlorides, dialkyl carbonates, and nitriles; (4) addition reactions involving aldehydes, ketones, imines, alkenes, and alkynes; and (5) Michael-type addition reactions to unsaturated aldehydes, ketones, imines, sulfoxides, sulfones, and nitro compounds. Finally, a section involving cyclization reactions is included for each of the six groups of nitrile-stabilized anions.
Keywords:
addition;
substitution;
nitriles;
anions;
scope;
limitations;
protected cyanohydrins anions;
halonitrile stabilized carbanions;
alkylations;
side reactions;
arylation;
vinylation;
acylation;
Michael acceptors;
ketones;
aldehydes;
Darzens reaction;
olefins;
nitrile stabilized carbanions;
sulfur substituents;
selenium substituents;
(dialkylkylamino)nitriles;
unsaturated nitriles;
experimental procedures
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