An “Anti-Baldwin” 3-Exo-Dig Cyclization: Preparation of Vinylidene Cyclopropanes from Electron-Poor Alkenes

Abstract

Stabilized carbanions undergo an uncommon 3-exodig cyclization onto propargyl halides through an SN2' substitution. Propargyl iodides as electrophiles are necessary to achieve good yields (36-95%) for most substrates, although the usefulness of chlorides and bromides is documented. A variety of monocyclic and bicyclic vinylidene cyclopropanes can be prepared. These products are not available by standard carbene methodology.

A palladium-catalyzed approach to allenic aromatic ethers and first total synthesis of terricollene A

“…As a class of synthetically useful chemicals, the versatile allenyl unit could be transferred into different structure units: Selenohydroxylation and oxidation of 3ga with 1-fluoropyridinium/1,2-diphenyldiselane could deliver 2-selenoenal 4 with a Z/E selectivity of 94/6; 14 Bromohydroxylation of this allenyl group in aqueous dioxane afforded terminal 2-bromoallylic alcohol 5 as the sole product in 72% yield; 15 The allenyl group may also be selectively transformed into corresponding primary allylic alcohol 6 with a E/Z selectivity of 98/2 by gold-catalyzed hydration reaction; 16 Iodination of allenyl group exclusively gave diiodide product (Z)-7 in 69% yield. 17 It should be noted that these products are difficult to synthesize through traditional transition-metal catalyzed coupling reactions. 10,18 Finally this method has been applied to the efficient syntheses of two naturally occurring allenes: eucalyptene A has been successfully synthesized under the catalysis of 5 mol% Pd(PPh 3 ) 4 in 90% yield from methyl 4-hydroxycinnamate and 2,3-butadienyl methyl carbonate (Scheme 2b); 70 mmol scale reaction of p-hydroxylmethylphenol with 1.14 equiv of 2,3butadienyl methyl carbonate 2a afforded the corresponding p- hydroxylmethylphenyl 2,3-butadienyl ether 10.…”

Effective synthesis of bicyclodienes via palladium-catalyzed asymmetric allylic alkylation and ruthenium-catalyzed cycloisomerization

“…Malonate 2a [49] was tested as a nucleophile with cyclopent-2-enyl benzoate 3a as an electrophile under different reaction conditions to obtain high enantioselectivity and yield of allylated malonate 4 (Table 1). Pd 2 (dba) 3 •CHCl 3 catalyzed the asymmetric allylic reaction in the presence of (S,S)-Trost-ligand (L std ) in THF in very good yield and very low enantioselectivity (entry 1, Table 1).…”

Lewis Acid‐Mediated Selective Cycloadditions of Vinylidenecyclopropanes with Aromatic Aldehydes: An Efficient Protocol for the Synthesis of Benzo[c]fluorene, Furan and Furo[2,3‐b]furan Derivatives

“…[10,11] We thought that the presence of functional groups may facilitate the selective cleavage of C À C bonds of VCPs, thus delicately tunning the regio-and stereoselectivity of the reactions. As a matter of fact, we found the reaction gave another interesting product, 7a, under similar conditions when the functionalized VCPs 6a was employed as substrate [Eq.…”