A New Simple Procedure for the Synthesis of Heptamethyl Cyclohepta-1,3,5-triene-1,2,3,4,5,6,7-heptacarboxylate

Abstract

A new and simple procedure for the synthesis of heptamethyl cyclohepta-1,3,5-triene-1,2,3,4,5,6,7-heptacarboxylate in a 51% yield is presented. An optimization of the reaction conditions was performed, and a convenient protocol for the isolation of the reaction product was developed. The structure of the key electrophilic intermediate was determined by means of NMR spectroscopy, and a plausible reaction mechanism is proposed.

Synthesis of Diazanorcaradienes and 1,2‐Diazepines via the Tandem [4+2]‐Cycloaddition/Retro‐[4+2]‐Cycloaddition Reaction between Methoxycarbonylcyclopropenes and Dimethoxycarbonyltetrazine

“…Our previous investigations of polyunsaturated cyclic molecules abundant with electron‐withdrawing groups revealed their rich reactivity towards either nucleophilic or electrophilic reagents as well as in the pericyclic reactions . One of the key synthons therein was 1,2,3,4,5,6,7‐hepta(methoxycarbonyl)cycloheptatriene (HMCH),, as well as its closely related carbocyclic analogs, relatively high acidity of HMCH being one of the key properties determining its high reactivity . Electron‐deficient 1,2‐diazepines are analogues of HMCH in which the two C–CO 2 Me moieties are substituted with nitrogen atoms which similarly stabilize the negative charge.…”

Synthesis of 1,2,3,4,5‐Penta(methoxycarbonyl)cyclopentadienides through Electrocyclic Ring Closure and Ring Contraction Reactions

“…[14] Moreover, we found that the reaction does not occur in the presence of other bases apart from pyridine (triethylamine, potassium acetate). Furthermore, we have recently shown [15] that hepta(methoxycarbonyl)cycloheptatriene 4 (HMCH) is formed in the reaction of N-(methoxycarbonylmethyl)pyridinium and either dimethyl dibromosuccinate 5 or bromomaleate 6 in the presence of pyridine. [15] Therein we provided the evidence that the key electrophilic intermediate in the formation of 4 is the di(methoxycarbonyl)vinylpyridinium ion 7.…”

“…Furthermore, we have recently shown [15] that hepta(methoxycarbonyl)cycloheptatriene 4 (HMCH) is formed in the reaction of N-(methoxycarbonylmethyl)pyridinium and either dimethyl dibromosuccinate 5 or bromomaleate 6 in the presence of pyridine. [15] Therein we provided the evidence that the key electrophilic intermediate in the formation of 4 is the di(methoxycarbonyl)vinylpyridinium ion 7. So, here we propose that the formation of cycloheptadienes 3a,b is similar to that of HMCH and includes intermediate 7.…”

“…Unless noted otherwise, all of the reagents were obtained from commercial suppliers and used without additional purification. HMCH ( 4 ) and dimethyl meso ‐2,3‐dibromosuccinate ( 5 ) were synthesized according to the literature procedures.…”

Synthesis of Indolizines from Pyridinium Salts and Ethyl Bromodifluoroacetate

“…Based on the above experimental observations and previous reports, , a plausible reaction mechanism for the synthesis of indolizines was proposed in Scheme . First, in the presence of Cs 2 CO 3 , the pyridinium salt would be deprotonated to afford ylide A which could capture the difluorocarbene to afford B .…”