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Ring Expansion of 2‐Alkylidenedihydroquinolines to 2‐Iminodihydro‐1‐benzazepines by Phenyl, Methanesulphonyl, and Trifluoromethanesulphonyl Azide [1]
Author(s) -
Quast Helmut,
Ivanova Svetlana,
Peters EvaMaria,
Peters Karl
Publication year - 2000
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/(sici)1099-0690(200002)2000:3<507::aid-ejoc507>3.0.co;2-v
Subject(s) - chemistry , cycloaddition , sodium azide , azide , ring (chemistry) , sodium hydride , alkyl , medicinal chemistry , deprotonation , nuclear magnetic resonance spectroscopy , thermal decomposition , yield (engineering) , stereochemistry , organic chemistry , ion , materials science , metallurgy , catalysis
2‐Alkyl‐1‐methylquinolinium hexafluorophosphates 1 are deprotonated by sodium or potassium hydride to afford solutions of 2‐alkylidenedihydroquinolines 2 , which are investigated by NMR spectroscopy. 1,3‐Dipolar cycloaddition of phenyl azide to 2 yields the spirocyclic products 10 . While, at 80‐110 °C, the [3 + 2] cycloaddition that afforded ( u )‐ 10f is reversible and accompanied by epimerisation to give ( l )‐ 10f , thermolysis of the dimethyl compounds 10b and d affords the ring‐expanded products 14b and d , respectively, in good yields along with molecular nitrogen. Irradiation of 10d with light of λ > 320 nm results in the formation of similar amounts of 14d and [3 + 2] cycloreversion products, viz. 2‐diazopropane ( 5b ) and the N ‐phenylimine 15d . ‐ Trapping of 2 by methanesulphonyl azide ( 18a ) gives mixtures of the products of ring expansion ( 21b , d ‐ f , 10‐50 %) and [3 + 2] cycloreversion ( 22a , d , 10‐80 %) of the apparently very labile intermediate spirocyclic cycloadducts 19 . The ratio of 21 vs. 22 is significantly improved when 18a is replaced by trifluoromethanesulphonyl azide ( 18b ), which affords the iminodihydrobenzazepines 21i ‐ k in 50‐75 % yield. The structures of the products are based on NMR evidence and X‐ray diffraction analyses performed with 21b , d , and ( ax,E )‐ 21e .