A. Le Coq

Reduction D′α,α′-dibromoorthoxylenes par les sels chromeux : generation facile d'orthoquino-dimethanes☆

Abstract α,α′-Dibromoorthoxylenes undergo a very fast reductive elimination on treatment with chromous chloride, affording the reactive intermediate orthoquinodimethanes which evolve into spiroorthoxylylenes 2 or may be trapped with dienophiles (adducts 3 and 4). Some attempts in the field of anthracycline precursors are reported.

Reduction par les sels chromeux de bromures benzyliques ortho-o-acyles avec transposition du groupement acyle: De l' ester : acces aux ortho-hydroxybenzyl cetones non masquees et une nouvelle preparation de benzo¦b¦furannes substitues en position-2

Abstract The σ-bonded organochromium (III) complexes resulting from the reduction of ortho -O-acyl benzylic bromides 1 with CrCl2., undergo an 1,5-transposition of the ester acyl functional group which allows, through selected experimental conditions either a selective access to the unmasked ortho -hydroxybenl ketones 2 or a new preparation of the 2-substituted benzo¦b¦furans 3 . The scope and limitations of the method are presented.

Réduction d'acétals γ-bromo α-acetyléniques par les sels chromeux: accès aux acétals et aldéhydes α-alléniques

Abstract Reduction of γ-bromo α-acetylenic acetals 1 with chromous ions (THF + HMPA) in the presence of AcOH affords α-allenic acetals 2 whose careful hydrolysis yields the corresponding aldehydes 3 . A new access to the dried bean beetle pheromone (racemic), via a Witting reaction with 3a is reported.