Studies on Electrophilic Interaction of 2,3‐Allenols with Electrophilic Halogen Reagents: Selective Synthesis of 2,5‐Dihydrofurans, 3‐Halo‐3‐alkenals, or 2‐Halo‐2‐alkenyl Ketones

Abstract

The reaction of primary 2,3-allenols with iodine (I 2 ) afforded 2,5-dihydrofurans while that of readily available 1-aryl or 1-methyl substituted 2,3-allenols with bromine (Br 2 ), N-bromosuccinimide (NBS), I 2 or N-iodosuccinimide (NIS) formed the not easily available but synthetically useful 3-halo-3-alkenals and 2-halo-2-alkenyl ketones with good selectivity and yields via a sequential electrophilic interaction of X + with the allene moiety, 1,2-aryl or 1,2-proton shift, and H + elimination process.

Copper (I) Iodide‐Catalyzed One‐Step Preparation of Functionalized Allenes from Terminal Alkynes: Amine Effect

“…When the reaction was complete after being stirred at 130 °C for 8 h as monitored by TLC upon cooling (during the reaction, prop‐2‐yn‐1‐ol was consumed quickly and the corresponding propargylic amine was produced, which was then transformed to the allene product at a relatively slow rate), the reaction mixture was cooled to room temperature and then filtered. Evaporation and column chromatography on silica gel afforded allene 2aa 8k as a liquid (eluent: petroleum ether/ethyl acetate=20/1, then 10/1); yield: 70 mg (41%). 1 H NMR (300 MHz, CDCl 3 ): δ =5.35–5.18 (m, 2 H, 2×CCH), 4.08 (dd, J =5.4, 3.0 Hz, 2 H, OCH 2 ), 2.06–1.92 (m, 3 H, OH and CH 2 ), 1.50–1.10 (m, 10 H, 5×CH 2 ), 0.92–0.79 (m, 3 H, CH 3 ); 13 C NMR (75.4 MHz, CDCl 3 ): δ =203.0, 93.7, 91.6, 60.7, 31.8, 29.1, 29.04, 28.97, 28.6, 22.6, 14.0; MS (EI): m/z =135 (M + −H 2 O−CH 3 , 0.72), 121 (M + −H 2 O−C 2 H 5 , 3.24), 55 (100); IR (neat): ν=3313, 2956, 2925, 2855, 1964, 1463, 1378, 1212, 1136, 1012 cm −1 ; HR‐MS (EI): m/z =168.1515, calcd.…”

Deciphering the Chameleonic Chemistry of Allenols: Breaking the Taboo of a Onetime Esoteric Functionality

“…Ma and collaborators have pioneered halogen-promoted 1,2-aryl shift, and 1,2-H shift in allenol skeletons. 320 , 321 Thus, secondary and tertiary allenols were reported to smoothly generate 3-halo-3-alkenals and 2-halo-2-alkenyl ketones respectively, under halogenating reagents such as Br 2 , I 2 , NIS, or NBS. During the past decade, related halogen-promoted 1,2-bond migrations in allenol systems have been employed in ring expansion processes.…”

Solvent-Controlled Switching of Cycloisomerization to Transposition in the Ag/Cu-Promoted Reaction of Terminal α-Allenols

“…Ma et al [10,11] described the electrophilic interaction of allenols where they explained the formation of 3-halo-3-alkenals by means of a new synthetic protocol, using α-allenols and X+ as the reaction substrate.…”