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Cycloadditions, 43 [1] . Cyclobutanones via Photoreactions of Chromium‐Carbene Complexes with Olefins and Dienes – A Comparison with the Traditional Ketene Method
Author(s) -
Köbbing Stephan,
Mattay Jochen,
Raabe Gerhard
Publication year - 1993
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.19931260816
Subject(s) - ketene , chemistry , cycloaddition , carbene , medicinal chemistry , stereoselectivity , dimer , yield (engineering) , olefin fiber , chromium , double bond , photochemistry , organic chemistry , catalysis , materials science , metallurgy
Photolysis of chromium‐carbene complexes 1 in the presence of olefins and dienes yields cyclobutanones 4 and 5 with varying stereoselectivity. Under oxidative conditions lactones 6, 7, 8 , and 10 are obtained as byproducts. Thermal reactions of ketenes 3 with olefins and dienes yield the same cyclobutanones with usually equal selectivities. In the case of 2,3‐dihydro‐1,4‐dioxin as olefin, diene 9 is obtained as a byproduct. Cycloaddition reactions of 1a or 3a with 1,2‐dimethylenecyclopentane ( 11 ) yield the spirocyclic cyclobutanones 12 and 13 . The symmetric ketone 16 and the ketene dimer 17 are formed as additional products upon cycloaddition of ketene 3b to tetraethoxyethylene. Novel α‐(butylthio)cyclobutanones 4j, k, l, m and 5k, l are formed by cycloaddition reactions of the newly prepared compounds 1c and 3c . The ketene dimer 20 is formed by thermal reactions of 3a with olefins. Unusually low stereoselectivities are observed in the case of photolytic reactions of 1c with dienes.