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  • 1
    ISSN: 1434-193X
    Keywords: Indiumallyl compounds ; Vinylcyclopropanes ; α,β-Unsaturated carbonyl compounds ; Diastereoselectivity ; Dibenzylideneacetone ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Allylindium reagents, prepared from excess allylic halide (Br or I) and indium metal, react with α,β-unsaturated ketones and aldehydes to give, after aerobic acidic workup, homoallyl-substituted vinylcyclopropanes. This process was explored and developed after a chance discovery arising from a side reaction in an attempted Pd-catalysed process. The structure of the cyclopropane arising from the reaction of bis(p-chlorobenzylidine)acetone was confirmed by X-ray crystallography. Whilst bis-α,β-unsaturated ketones give rise to a single homoallylcyclopropane species, α,β-unsaturated ketones and aldehydes give diastereomeric mixtures whose relative stereochemistry were assigned by NOE experiments. Crotylindium reagents react with good to perfect regioselectivity to afford tetrasubstituted cyclopropanes but prenylindium reagents fail to generate the analogous pentasubstituted rings.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1434-193X
    Keywords: Indium ; Vinylcyclopropanes ; Ring closing metathesis ; Norcarenes ; Kinetic diastereoselection ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Homoallyl-substituted vinyl cyclopropanes 1a-c, which are readily prepared by reaction of allylindium reagents with α,β-unsaturated ketones and aldehydes, undergo Ru-catalysed RCM reactions with Grubbs catalyst to give [4.1.0]bicyclooct-2-ene (norcarene) type bicyclic products. Noncyclisable ‘trans’ homoallyl-substituted vinyl cyclopropanes 1b and 1c are separated from their ‘cis’ diastereomers by RCM to 5b and 5c - but only with moderate efficiency due to a competing homo-cross metathesis (‘dimerisation’) to give 7b and 7c, respectively. However, the four diastereomers of the (homoallyl)distyrylcyclopropane 14a obtained from indium-mediated reaction of dibenzylideneacetone and crotyl bromide undergo remarkable kinetic diastereoselection in their RCM reactions to give a 4,7-dimethyl[4.1.0]bicyclohept-2-ene-type product 15a. This process allows recovery of a single diastereomer (〉 95%) of 14a without dimerisation being a significant side reaction. Furthermore, the RCM product 15a is obtained rich in one diastereomer (ca. 90%). The kinetic diastereoselection and lack of dimerisation can be rationalised by considering developing transannular interactions and a pseudo-A1,3 strain model.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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