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On the Thermal Cycloisomerization of Long‐Chain Alkylacetylenes in the Gas Phase
Author(s) -
Ondruschka Bernd,
Zimmermann Gerhard,
Remmler Matthias,
Ziegler Ulrich,
Kopinke FrankDieter,
Olk Bernhard,
Findeisen Matthias
Publication year - 1989
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19891220419
Subject(s) - chemistry , cycloisomerization , cyclopentene , acetylene , gas phase , photochemistry , stereochemistry , medicinal chemistry , organic chemistry , catalysis
The thermal cycloisomerization of some alkylacetylenes was investigated in a tubular quartz reactor. At 570°C 1‐hexyne ( 1 ) rearranges to 3‐methyl‐1‐cyclopentene ( 5 ) with a selectivity of about 27 by a reaction sequence including an acetylene‐vinylidene rearrangement and 1,5‐C,H insertion of the intermediately formed alkylidenecarbene species. 5‐methyl‐1‐hexyne ( 2 ) behaves analogously forming 3,3‐dimethyl‐1‐cyclopentene ( 6 ), while 2‐hexyne ( 3 ) provides 1‐methyl‐1‐cyclopentene ( 7 ) indicating that the acetylene‐vinylidene rearrangement is obviously not restricted to 1,2‐H shifts. The mechanism of the cycloisomerization of alkylacetylenes is investigated by means of D‐labeled parent alkynes. The results show that the unimolecular cycloisomerization via alkylidenecarbenes obviously can be an important channel despite the dominance of a radical chain course.