The preparation of several 1,2,3,4,5-functionalized cyclopentane derivatives

Abstract

SummaryWith the goal of eventually synthesizing [5]radialene (3), the still missing member of the parent radialene hydrocarbons, we have prepared the pentaacetates 21 and 31, the pentabromide 29 and the hexabromide 32. In principle these should be convertible by elimination reactions to the desired target molecule.

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

“…1,1,2,3,4,5,6,7‐Octa(methoxycarbonyl)cyclohepta‐2,4‐diene (3a) and 1,1,2,3,4,5,6,7‐Octa(methoxycarbonyl)cyclohepta‐3,5‐diene (3b): A mixture of dimethyl dibromosuccinate 5 (3.45 g, 11.4 mmol), dimethyl malonate (0.50 g, 3.8 mmol), pyridine (1.8 g, 22.7 mmol), and DMF (1.8 mL) stirred for 3 d. The mixture was poured into water (10 mL), decanted and the precipitate was stirred with diethyl ether (10 mL), filtered and washed with water and ether to give the desired mixture of cycloheptadienes 3a , 3b (1.08 g, 52 %). The physical data correspond to those previously reported …”

“…We have shown herein that DMAD ( 2 ), which is conventionally used for the generation of vinylpyridinium 7 , could be substituted with dimethyl dibromosuccinate 5 in the reaction with dimethyl malonate to give the mixture of tautomeric cycloheptadienes 3a , b in a yield of 52 %. It is noteworthy that the ratio of tautomers 3a , b depends to a large extent on the work‐up as it was previously noted for the conventional syntheses . DMAD is polymerizable, lachrymatory and vesicant while dimethyl dibromosuccinate is a crystalline, non‐volatile substance, which is easily available from cheap succinic acid.…”

“…The conventional method for the preparation of PMCP 1a includes the reaction of dimethyl acetylenedicarboxylate 2 (DMAD) and dimethyl malonate in the presence of catalytic pyridine and acetic acid to form a mixture of isomeric cycloheptadienes 3a , b , which are subsequently transformed into 1a by heating with potassium acetate in water (Scheme ) . Le Goff and LaCount suggested that the mechanism includes a nucleophilic attack of dimethyl malonate in a nucleophilic form onto a DMAD molecule, but no evidence was provided in support of that claim .…”

“…The conventional method for the preparation of PMCP 1a includes the reaction of dimethyl acetylenedicarboxylate 2 (DMAD) and dimethyl malonate in the presence of catalytic pyridine and acetic acid to form a mixture of isomeric cycloheptadienes 3a,b, which are subsequently transformed into 1a by heating with potassium acetate in water (Scheme 1). [13] Le Goff and LaCount suggested that the mechanism includes a nucleophilic attack of dimethyl malonate in a nucleophilic form onto posed to be used instead of dimethyl acetylenedicarboxylate. A novel method for the synthesis of penta(methoxycarbonyl)cyclopentadienylsodium through the reduction of hepta(methoxycarbonyl)cycloheptatriene with sodium borohydride, electrocyclic ring contraction and retro-[2+2]-cycloaddition was developed.…”

“…Thus, the emergence of two singlets of the ester groups at δ = 3.90 and 3.68 ppm together with a vinyl proton singlet at 7.41 and pyridinium ring signals, which appear in the lower field to those of pyridine (all signals are colored red), indicate the presence of the intermediate proposed. It was also investigated by means of 13 C NMR spectroscopy and the signal assignment was accomplished by using HSQC and HMBC Scheme 2. Mechanism for the formation of cycloheptadienes 3a,b.…”