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Thermisches Verhalten von Cyclopropa[ c ]chromenen
Author(s) -
Hug R.,
Fráter Gy.,
Hansen H.J.,
Schmid H.
Publication year - 1971
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19710540130
Subject(s) - chemistry , conrotatory and disrotatory , ring (chemistry) , stereochemistry , deuterium , alkyl , closure (psychology) , medicinal chemistry , organic chemistry , physics , quantum mechanics , economics , market economy
The Cyclopropa[ c ]chromenes 14 , trans ‐and cis ‐ 15 , trans ‐and cis ‐ 16 and 17 rearrange on heating > 200° in N, N‐diethylaniline to give 2‐alkyl‐2 H ‐chromenes 7, 8, 21, 22. The rate determining step of this rearrangement is the ‘homoelectrocyclic’ ring opening of the cyclopro‐pa[ c ]chromenes to give ω‐allyl‐quinomethanes of type 4. These intermediates show fast [1,5 s ] and [1,7 a ] H‐shifts, followed by electrocyclic ring closure. Deuterium labelling experiments are in agreement with this mechanism. The remarkable dependence of the rates of rearrangement with respect to the stereochemistry of the cyclopropa[ c ]chromenes (cf. table 2) suggests that in the first step only one of the two possible disrotatory modes of ring opening is involved.