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Thermal Rearrangements of Bicyclopropylidene and Substituted Bicyclopropylidenes − A Gas Phase Kinetic and Product Study
Author(s) -
de Meijere Armin,
Kozhushkov Sergei I.,
Faber Dietmar,
Bagutskii Viktor,
Boese Roland,
Haumann Thomas,
Walsh Robin
Publication year - 2001
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/1099-0690(200110)2001:19<3607::aid-ejoc3607>3.0.co;2-f
Subject(s) - chemistry , cyclopropane , methylenecyclopropane , cyclopentene , yield (engineering) , arrhenius equation , methylene , flash vacuum pyrolysis , isomerization , derivative (finance) , cyclopentane , kinetics , pyrolysis , medicinal chemistry , stereochemistry , activation energy , organic chemistry , ring (chemistry) , thermodynamics , physics , financial economics , economics , catalysis , quantum mechanics
The gas phase thermal rearrangement of bicyclopropylidene ( 1 ) has been studied, and the pressure‐independent Arrhenius parameters determined as log( k /s −1 ) = (14.02±0.33) − (39.2±0.7) kcal·mol −1 / RT ·ln10, almost the same as those for methylenecyclopropane ( 2 ). Thus, the second cyclopropane ring in 1 exerts virtually no influence on the kinetics of the thermal rearrangement of one of its methylenecyclopropane subunits. The rearrangement of 1 to methylenespiropentane ( 5 ) was found to be reversible, with an equilibrium composition at 230 °C of 1:166. These findings are discussed and accounted for. When heated to 350 °C in a flow system, 1 undergoes a clean rearrangement to 5 [90% yield, ⩾ 95% purity on a preparative scale (17.4 g)]. Allyl‐ ( 7 ), ethenyl‐ ( 9 ), and ( E )‐(2‐methoxycarbonylethenyl)bicyclopropylidene ( 10 ) were prepared from 1 in 50, 45, and 69% overall yields, respectively. The thermal rearrangements of 9 and 10 proceeded smoothly at 150−160 °C, resulting in the formation of 4‐methylenespiro[2.4]hept‐5‐ene ( 14 ) and its derivative 17 in 79 and 50% isolated yields, respectively, as the sole products, while the rearrangement of 7 required higher temperatures (200 °C) and resulted in a complex mixture of isomeric substituted methylenespiropentanes 18 − 20 . Under flash vacuum pyrolysis conditions at 550 °C, the methylenespiroheptene 14 , initially formed from 9 via 1‐methylene‐2‐vinylspiropentane ( 13 ), underwent a further vinylcyclopropane‐to‐cyclopentene rearrangement to yield a 1:1 mixture of the isomeric tetrahydropentalenes 15 and 16 . This constitutes a novel and easy access to the tetrahydropentalene skeleton.