Electrophilic Cyclization of 2‐(2′,3′‐Allenyl)acetylacetates with Iodine Using Calcium Hydride as the Base

Abstract

A facile and efficient protocol for the synthesis of 4,5‐dihydrofuran derivatives via iodine‐mediated cyclization of various 2‐(2′,3′‐allenyl)acetylacetates with CaH2 as the base has been developed. The yields range from moderate to good. The resulting products can be used for further elaboration by palladium‐catalyzed coupling reactions.

Highlighting the Rich Chemistry of the Allenone Moiety

“…On the other hand, γ‐allenones 208 react through a selective 5‐ exo ‐ dig cyclization in the presence of molecular iodine generating dihydrofurans 209 b in good yields (Scheme 40b) [125] . Unsymmetrically substituted allenes at the terminal position have afforded mixtures of the two expected isomers, being Z ‐alkenes 209 b the preferred adducts (Scheme 40b) [125] …”

“…In a recent report, alkynones 205 in the presence of silver catalysts generate silver allenones 207 , which in situ undergo a formal [3+2] cycloaddition to yield highly strained dihydrofuran systems 206 as mixtures of anti/syn isomers (Scheme 40a) [124] . On the other hand, γ‐allenones 208 react through a selective 5‐ exo ‐ dig cyclization in the presence of molecular iodine generating dihydrofurans 209 b in good yields (Scheme 40b) [125] . Unsymmetrically substituted allenes at the terminal position have afforded mixtures of the two expected isomers, being Z ‐alkenes 209 b the preferred adducts (Scheme 40b) [125] …”

“…the preferred adducts (Scheme 40b). [125] Interestingly, a divergent chemical behaviour has been found under metal catalysis, providing both dihydrofuran and cyclopentene skeletons in different ratios depending on the experimental conditions. Thus, reaction of γ-allenones 208 c in the presence of aryl iodides as co-cyclization partners has provided dihydrofuran structures 208 c along with small amounts of cyclopentene derivatives 210 c (Scheme 40c).…”

Metal-free addition of aliphatic carboxylic acids to cyanopropargyl alcohols: an access to new families of functionalized dihydrofurans and 3(2H)-furanones

“…11,[19][20][21] For this purpose, the ring closing reaction of 1,3-dicarbonyl compounds with alkenes is efficient as well. [22][23][24][25] Cyclization of the but-3-yn-1-ols is also a method of choice for the synthesis of 2,3dihydrofurans. [26][27][28][29] Recently, a method for the preparation of functionalized 2,3-dihydrofurans by Sc(OTf) 3catalyzed cyclization of α-allylated 1,3-dicarbonyl compounds has been reported.…”

Electrophilic Cyclizations of Diaryl-2,3-allenyl Ethers withN-Bromosuccinimide: En Route to 2-Bromonaphthalenes

“…Electrophilic cyclization reactions of allenes have been well established for the synthesis of important unit in organic synthesis. − The most extensively studied ones are the electrophilic reaction of allenes with X + (X = Cl, Br, I, RSe), followed by the attack of intramolecular oxygen nucleophiles for the construction of the C–O bond: − The reaction of 2,3-allenols with X + could afford 3-halo-2,5-dihydrofurans with good to excellent yields; 2,3-allenoates and 2,3-allenoic acids can also easily undergo an electrophilic cyclization reaction affording β-halobutenolides; 4,5-dihydrofuran and furan derivatives were synthesized via electrophilic cyclization of allenyl ketones with electrophilic reagents; furthermore, the electrophilic cyclization could also offer an efficient strategy for the formation of aza- and other heterocyclic compounds . Therefore, the feasibility of using carbon nucleophiles could be an entry for the formation of C–C bonds.…”