Umlagerung von α‐Halogen‐ in α′‐Halogen‐cyclobutanone, Schlüsselstufe einer variationsreichen Synthese von Pyrethroiden

Abstract

Rearrangement of a-Halogen-to a '-Halogen-cyclobutanones, Key Step of a Highly VersatileSynthesis of Pyrethroids Summary a-Halogenocyclobutanones, which are readily available by [2 + 21-cycloaddition of haloketenes to terminal olefins (e. g . 5 + 6), undergo an efficient and stereoselective cine-rearrangement to a'-halogenocyclobutanones in the presence of catalysts such as tertiary amines, HX acids or quaternary ammonium salts (e. g . 6 -+ 7, Table I). Preparative as well as mechanistic aspects of the cine-rearrangement are discussed. The 2,4-cis-disubstituted cyclobutanones 7-32 thus formed represent valuable intermediates in a new synthesis of pyrethroids 1. The X-ray structure of 2-chloro-4-(2,2,2-trichloroethyl)-3,3-dimethylcyclobutanone (7), the most important precursor of cis-3 (X = Cl) shows the following features : a puckered cyclobutanone ring (dihedral angle 3 I O), 2,4-cis-di-pseudoequatorial arrangement of the chloro and trichloroethyl substituents, and an endo-deviation (0.225 A; 11") of the carbonyl 0-atom from the plane formed by C( l), C(2) and C(4) (Fig. 2).

Catalytic asymmetric synthesis of cyclopropanecarboxylic acids: an application of chiral copper carbenoid reaction

“…In Ciba-Geigy's cis-permethrinic acid synthesis (ref. 23), stability of the four-membered intermediate, cis-2-chloro-3, 3-dimethyl-4-trichloroethyl-cyclobutanone is ascribed to a puckered conformation of cyclobutanone ring to release repulsion of two substituents at the 2,4-cis positions.…”

Cycloaddition and Electrocyclic Reactions of Vinylketenes, Allenylketenes, and Alkynylketenes

“…67 Halogenated cyclobutanones formed in this way are useful intermediates in the synthesis of insecticidal pyrethroids. The cyclobutenone is the preferred isomer in the equilibrium process, and perchlorovinylketene generated in the absence of the alkene by a dealkylation-elimination method undergoes ring closure (Scheme 34).…”

“…68 Ring closure to the cyclobutenone is favored by the destabilizing effect of the α-chlorine of the ketene plus the stabilizing effect, by π-donation to the carbonyl, of chlorine at C3 of the cyclobutenone. 67 neat, sealed tube, 160°O …”

Base‐Induced Trifluoroethanolysis of Acyclic Di‐ and Trihalogeno Ketones: Favorskii Rearrangement and [4+3] Cycloaddition

“…[34] Analogous α Ǟ αЈ rearrangements have been observed with α-halogenocyclobutanones and called cinesubstitution, [35] and cine-rearrangement, respectively. [36] The solvolysis of the primary cycloadduct(s) cannot occur when the oxyallyl intermediate(s) are generated in lithium perchlorate/diethyl ether. [11,12] However, in this solvent the reaction between 30 and furan, in the presence of triethylamine, gave only a 23 % yield of the expected dichlorooxabicycles.…”

“…[2] The same stereoselectivity was found for "classical" Favorskii rearrangements with bases in water where, e.g., 1,1,3-trihalogenobutan-2-ones 24 and 25, leading to 2,4-dihalogenated 8-oxabicyclo[3.2.1]oct-6-en-3-ones (26,27) as a mixture of endo-exo-stereoisomers. With trichloromethyl isobutyl ketone (30) the isomeric 2,4-dichloro-substituted oxabicycles (34) were formed in lithium perchlorate/diethyl ether/ furan/triethylamine, while in NaTFE/TFE solvolytic displacement of one chloro substituent occurred, providing 2-chloro-4-trifluoroethoxy-4-isopropyl-8-oxabicyclo[3.2.1]oct-6-en-3one (36). By analogy, 27 reacted with sodium methoxide/ methanol to form the methoxy-substituted oxabicycles 39a and 39b.…”