Halogen-Substituted Allenyl Ketones through Ring Opening of Nonstrained Cycloalkanols

Abstract

An efficient synthesis of halogen-substituted allenyl ketones via Ag-catalyzed oxidative ring opening of allenyl cyclic alcohols under mild reaction conditions has been achieved. The reaction features a wide substrate scope and excellent regioselectivity. The synthetic potential of the products has been demonstrated by their conversion to stereodefined alkenes and heterocyclic compounds.

Rearrangements of the Chrysanthenol Core: Application to a Formal Synthesis of Xishacorene B

“…In both cases, the only observed rearrangement was to [3.1.1]­bicycle 12V in the vinyl case (Figure C), or nonspecific decomposition of the starting material. Given numerous emerging studies of the unusual reactivity of allenol-bearing substrates compared to their vinyl analogues, , we sought to examine the reactivity of the allenyl adduct of chrysanthenol ( 10A , Figure ) under conditions that would generate the magnesium alkoxide, as outlined in Figure . The calculations described above suggested that the energy for C–C bond homolysis of 10A would lie between that of the vinyl and alkynyl chrysanthenol adducts ( 10V and 10P , respectively).…”

An Alternative Route to Complex Allenes or Cyclooctatrienes via a Suzuki Cyclocarbopalladation Cascade

“…For example, in 2019, Ma and coworkers reported the arylation of propargylic carbonate 6 with arylboronic acid in presence of Pd 2 (dba) 3 ⋅ CHCl 3 , P(o‐Tolyl) 3 in THF at room temperature (Scheme 2) giving high yields of allenes 7 [8] . Other work by the same group recently introduced the enantioselective synthesis of axially chiral allenes using the same methodology [9] . Our initial goal was to apply the Suzuki coupling to broaden the scope of the chemistry leading to 3 , creating a new type of molecular scaffold containing, inter alia, an allene functional group.…”

“…[8] Other work by the same group recently introduced the enantioselective synthesis of axially chiral allenes using the same methodology. [9] Our initial goal was to apply the Suzuki coupling to broaden the scope of the chemistry leading to 3, creating a new type of molecular scaffold containing, inter alia, an allene functional group. The first conditions applied to 1 a were the following, boronic acid 8 1.2 equiv., Pd(OAc) 2 5 mol%, PPh 3 10 mol%, NaOH 1.5 equiv., THF, 100 °C MW, 1 h.…”

“…These optimized conditions were then Scheme 2. Ma [9] synthesis of allenes via Suzuki addition Table 1. Optimization of the formation of substituted allenes.…”

Electrophotochemical Ring-Opening Bromination of tert-Cycloalkanols

“…The groups of Shi and Wang developed alternative methods avoiding the use of Br 2 , consisting of chemical oxidants and bromide salts, such as phthaloyl peroxide/Bu 4 NBr and PhI­(OAc) 2 /NaBr, with visible light irradiation. In addition to the stoichiometric reaction, transition-metal-catalyzed reactions using iridium-based photoredox catalysts or silver salt have been also utilized for the ring-opening halogenation of unstrained tert -cycloalkanols (Scheme a, bottom). Despite recent progress in the field of the ring-opening halogenation of unstrained tert -cycloalkanols, reported protocols require the use of (super)­stoichiometric amounts of chemical oxidants or expensive transition-metal catalysts.…”