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Chromium Complex Catalyzed Synthesis of Spirocyclopropanes from Diaryl Diazo Compounds – Direct NMR‐Spectroscopic Observation of a Carbene Complex Intermediate
Author(s) -
Pfeiffer Jürgen,
Nieger Martin,
Dötz Karl Heinz
Publication year - 1998
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(199806)1998:6<1011::aid-ejoc1011>3.0.co;2-h
Subject(s) - chemistry , cyclopropanation , diazo , carbene , medicinal chemistry , cycloaddition , enol ether , diphenyl ether , metathesis , double bond , regioselectivity , photochemistry , organic chemistry , catalysis , polymer , polymerization
The [2 + 1] cycloaddition reaction of electron‐rich alkenes such as enol ethers with 9‐diazo‐9 H ‐fluorene ( 1 ) is efficiently catalyzed by pentacarbonyl(η 2 ‐ cis ‐cyclooctene)chromium(0) ( 2 ). This cyclopropanation reaction shows a pronounced preference for electron‐rich CC bonds, as demonstrated by the regioselective reactions of allyl vinyl ether and 2‐vinyloxyethyl acrylate; the [2 + 1] cycloaddition proceeds via the carbene complex intermediate 13 , which has been detected by 13 C‐NMR spectroscopy in the course of the reaction. ( Z )‐Propenyl benzyl ether yields spirocyclopropane 21 with retention of the configuration of the former olefinic double bond. Whereas diazo compounds 22 and 23 react with ethyl vinyl ether to give low yields of cyclopropanes, the dibenzocycloheptenylidene and diarylcarbene precursors 24 and 25 afford moderate yields of olefin metathesis products 29 – 31 . The competition between cyclopropanation and olefin metathesis reflects the propensity of the carbene complex intermediates to undergo decarbonylation.