title: A new highly efficient three-component domino Heck-Diels-Alder reaction with bicyclopropylidene: rapid access to spiro[2.5]oct-4-ene derivatives.
abstract: Bicyclopropylidene (1) was found to surpass even methyl acrylate (17 a) in its rate of undergoing carbopalladation with aryl- or alkenylpalladium species, leading to substituted allylidenecyclopropanes 5, 7 and 10, mostly in high yields (37-78 %). These dienes and cross-conjugated trienes react in a Diels-Alder mode with dienophiles to give spiro[2.5]octenes 18 a-Ph, 18 b-Ph and 18 a-Vin, respectively, in good yields (89, 69 and 65 %). The overall transformation can be achieved as a one-pot three-component reaction with a variety of dienophiles to furnish the domino Heck-Diels-Alder products 18 regioselectively in most cases in good to very high yields (49-100 %). The reaction of 1 with iodobenzene (2-Ph) and 17 a gave 18 a-Ph in virtually quantitative yield-also on a gram scale-using only 1 mol % of catalyst, and even bromobenzene (22) gave 18 a-Ph in 59 % yield. Bicyclopropylidene (1), in the presence of palladium acetate/triphenylphosphane underwent rearrangement to allylidenecyclopropane (5-H), which in turn dimerized (73 %) in the absence of other reaction partners, or could be trapped by diethyl fumarate (17 c) to give the Diels-Alder adduct 18 c-H in 45 % yield. The coupling of oligoiodobenzenes with 1 and subsequent cycloaddition could be extended to a multicomponent reaction. In this way, 1,4-diiodobenzene (37), 1 and an alkyl acrylate gave the products 38 of a twofold Heck-Diels-Alder reaction in up to 87 % yield, 1,3,5-triiodobenzene (39) reacted in up to 72 % yield and ultimately 1,2,4,5-tetraiodobenzene (41) gave the fourfold domino Heck-Diels-Alder product 42 in 47 % isolated yield, in a single operation in which 12 new carbon-carbon bonds were formed.
authors.affiliation: Institut für Organische Chemie, der Georg-August-Universität Göttingen, Tammannstrasse 2, 37077 Göttingen, Germany.
authors.forename: Hanno
authors.initials: H
authors.lastname: Nüske
authors.forename: Stefan
authors.initials: S
authors.lastname: Bräse
authors.forename: Sergei I
authors.initials: SI
authors.lastname: Kozhushkov
authors.forename: Mathias
authors.initials: M
authors.lastname: Noltemeyer
authors.forename: Mazen
authors.initials: M
authors.lastname: Es-Sayed
authors.forename: Armin
authors.initials: A
authors.lastname: De Meijere