Alkyl Aluminum Halide Promoted Intramolecular Cyclization of ω‐Allyl‐cycloalk‐2‐enones: Access to Bridged Bi‐ and Tricyclic Compounds

Abstract

Durch Cyclisierung zu Duft: Die Umlagerung von ω‐Allylcycloalkenonen liefert in guten Ausbeuten strukturell komplexe bi‐ und tricyclische Ketone (siehe Schema). Auf diesem Weg ist eine olfaktorisch interessante Verbindungsklasse effizient zugänglich.

Novel Rearrangements of Guaiane Sesquiterpenes

“…The mechanistic proposal of this reaction involves a number of consecutive 1,2-H and alkyl shifts as depicted in Scheme 1. [19] We assume that the aluminum catalyst polarizes the endocyclic double bond of 13 form the convex side of the molecule, generating a more cationic β-carbon bond center to which the isopropenyl group adds, forming intermediate II. A 1,2-alkyl shift to intermediate III, followed by a 1,2-H shift to IV subsequently occurs in which the H-atom at the 1 position of 13 epimerizes to 14 and 16.…”

“…The mechanistic proposal leading to this compound can be rationalized by an initial activation of the double bond of the isopropenyl group of bulnesene, spawning zwiterionic intermediate complex V. After transanular cyclization to intermediate VI, an 1,2-alkyl shift to VII occurs, in which the cation is quenched by the vicinal aluminate to form the three-membered ring of the final product 18. Interestingly, this compound shares the overall constitution and stereochemical topology of patchoulol (19) which may become accessible from bulnesene, should hydroxylation of the cation in an intermediate like VII become feasible.…”

“…85 °C -150 °C, 0.12 bar) to yield 20 as a colorless oil (2.83 g, 58 %). (19), 81 (18),67 (7), 55 (15), 41 (16).…”

“…13 C-NMR (150 MHz, C 6 D 6 ): 225.0 (s), 60.0 (d), 59.0 (s), 48.9 (d), 46.6 (d), 39.8 (d), 38.0 (t), 36.4 (d), 35.6 (t), 35.0 (t), 33.9 (t), 32.9 (t), 23.0 (q), 16.0 (q), 15.8 (q) ppm. GC/MS (EI): m/z (%): 220 (14) [M + ], 202 (1), 191 (1), 177 (3), 162 (100), 147 (19), 135 (9), 121 (16), 107 (22), 95 (25), 81 (26), 55 (32), 41 (27) To a solution of aldehyde 28 (0.5 g, 2.124 mmol) in tbutanol (21 mL) was added powdered KOH (0.216 g, 3.85 mmol). O 2 was bubbled (0.5 bar) through the solution under vigorously stirred (900 rpm) for 1 h. The mixture was diluted with 30 mL dist.…”

Expanding the frontier of gold-catalyzed cyclizations and rational ligand design.

“…[82][83][84][85][86][87] To probe the reactivity of alkynylenolates, we speculated that the Michael addition of allenic ketones to vinyl ketones could yield 2-alkynyl 1,5-diketones, triggering an intramolecular aldol reaction leading to the formation of hydroxycyclohexanones or cyclohexenones in tandem fashion. [190][191][192][193][194][195][196] the synthetically more interesting 2-alkynylsubstituted analogs have been rarely reported in the literature.…”