Synthesis of Donor–Acceptor Alkynylcyclopropanes by Diastereoselective Cyclopropanation of Electron‐Deficient Alkenes with Alkoxyalkynyl Fischer Carbene Complexes

Abstract

The reaction of electron-deficient alkenes with alkoxyalkynyl Fischer carbene complexes (FCCs) represents a straightforward route to a new type of captodative (donor-acceptor) alkynylcyclopropanes, which have been prepared in moderate to high yields and in a diastereoselective manner. Some studies regarding the employment of additives to facilitate the recovery of the metal moiety after the reaction are also described. Finally, the first example of a cyclopropanation reaction through employing Fischer carbene complexes under microwave irradiation is presented; this method proved to be an advantageous alternative to the thermal reaction.

Gold‐Catalyzed Cycloisomerizations of Functionalyzed Cyclopropyl Alkynes: the Cases of Carboxamides and Alcohols

“…In this way we have been able to prepare six-membered heterocycles (pyridines and dihydropyridones) [4] and carbocycles (phenols and terphenyls) [5] from push-pull conjugated dienynes. We hypothesised that readily accessible push-pull alkynyl cyclopropanes 1 and 2 [10,11] could be suitable starting materials for a cascade reaction consisting on a sequential intramolecular nucleophilic addition/cyclopropane ring-opening (Figure 1). [8,9] Taking into account our previous experience, we wanted to assess the influence of donor-acceptor substituents in the cyclization of this kind of substrates.…”

Domino [2+2]/[2+1] and [3+2]/[2+1] Reaction Sequences of Alkynyl(alkoxy) Chromium Fischer Carbene Complexes

“…However, the [2+2]/[2+1] reaction took place successfully for aromatic substituted alkynyl FCCs 1c-h, and the moderate yields reached are in the usual range for most of the cyclopropanations involving alkynyl FCCs. [6] Thus, electronwithdrawing-( [12] Again, four diastereomers were generally obtained, the cis-isomers being the major ones, except for FCC 1h where only two diastereomers of 4h were observed and the same stereochemistry as for the other adducts was assumed ( for the major diastereomers of 4a: this result indicates a cisrelationship between the cyclopropane-fused tetrahydrofuran ring and the -OMe group for both major diastereomers ( Figure 1). An X-ray structure for cis-4g-min, [13] [11] [g] Only two diastereomers were detected; dr determined by integration of the MeO-signal.…”

“…For the formation of 10, the reagents were mixed together at room temperature and, once the TLC indicated disappearance of 1a, warmed to 70°C. By employing this procedure the possible cyclopropanation of methyl acrylate as a side reaction [6] was minimized. However, for the synthesis of 9, 2,3-dihydrofuran was added at a later stage, to avoid its [2+2] cycloaddition to 1a.…”

“…[5] Very recently, we found that alkynyl FCCs 1 react with electron-deficient alkenes when heated in THF, in a sealed tube at 90°C, to produce captodative alkynylcyclopropanes 2 in moderate-to-good yields (Scheme 1). [6,7] When we tested the reaction conditions by warming 1a with an electron-rich olefin such as 2,3-dihydrofuran (3a), we obtained adduct 4a as the major reaction product, as a mixture of diastereomers.…”

Up to Seven‐Component Adducts by Unprecedented Multiple Alkyne and Carbonyl Insertions in the Metal–Carbon Bond of Chromium Alkoxy Alkynyl Carbene Complexes

“…All common reagents and solvents were obtained from commercial suppliers and used without any further purification unless otherwise indicated. Fischer carbene complexes 1 a, [19] 1b, [20] 1 c, [21] 1d, [22] 1 e and [23] 1f, [24] were prepared by following described procedures. Alkynes 2 are commercially available and were used as received, without further purification.…”