Chemistry of carbanions. 31. Cyclization of the metal enolates from .omega.-bromo ketones

Abstract

Utilizing stable solutions of i-PrzNLi in hexane, a convenient procedure is described for the conversion of methyl w-bromoalkyl ketones 9-12,32,42,50, and 67 to mixtures of Li+ enolates containing predominantly the terminal enolates. Although solutions of these Li+ enolates in EtzO-hexane mixtures are stable a t 0 "C, when activating ligands such as 4 molar equiv of HMP [(MezN)sPO], 1 molar equiv of triglyme (15) or the 14-crown-4 ether 16, or excess DME are added these Li+ enolates undergo intramolecular cyclization reactions. In the absence of serious geometrical con!straints (cf. bromo ketone 32), the enolates of bromo ketones 9-12 underwent intramolecular C-alkylation to form the corresponding cyclohexanone derivatives in 60-80% yield. Similar intramolecular cyclization by bromo ketone 67 produced a mixture of five-membered and seven-membered C-alkylated products, but intramolecular cyclization of the bromo ketone 42 yielded only the five-membered 0-alkylated product 43. The Li+ enolate of bromo ketone 50 underwent a very slow intramolecular cyclization to produce a mixture of 0-alkylated and Calkylated four-membered ring products. Thus, the method described constitutes a useful synthetic route to cyclohexanone derivatives and, with limitations, is also applicable to the synthesis of cycloheptanone derivatives. n Br 5 i 7 0 1978 American Chemical Society Br 6 1 8 Metal Enolates from w-Bromo Ketones

Reactions involving electron transfer. 12. Effects of solvent and substituents upon the ability of lithium diorganocuprates to add to enones

“…25 (2 H, s, CH2CO), 2.04 (3 H, s, CH3CO), and 0.8-1.5 (15 H, m, aliphatic CH including a CH3 singlet at 0.97); mass spectrum m/e (rel. intensity) 156 (M+, <1), 98 (35), 69 (30), 58 (14), 57 (36), 56 (22), 43 (100), and 41 (16). The natural abundance 13C NMR spectrum of the ketone 22 (CDC13) is summarized in the following formula; the indicated assignments are consistent with off-resonance decoupling measurements.…”

An Intramolecular Allenic [2 + 2 + 1] Cycloaddition

“…Alkynyl allenes 25 , 28 , and 31 were prepared using a method developed in our laboratories for the direct conversion of ketones to allenes . The conjugate addition of organomagnesium reagent 36 to 1-acetyl-1-cyclopentene and 1-acetyl-1-cyclohexene was effected using catalytic manganese(II) chloride (30%) and copper(I) chloride (3%) followed by an in situ trap of the enolate with diethyl chlorophosphate to afford the desired enol phosphates (Scheme ). Elimination of the phosphate to give the allene is then carried out by the addition of LDA at low temperature.…”

Short Synthesis of Oxetane and Azetidine 3-Aryl-3-carboxylic Acid Derivatives by Selective Furan Oxidative Cleavage

“…To date, there are very few examples of 3-aryloxetane-3-carboxylic acids in the literature due to the lengthy and low-yielding methods for their preparation (see the SI for further details), and the few commercially available examples are expensive . The synthesis of the corresponding 3,3-disubstituted azetidines and 1,1-disubstituted cyclobutanes has been somewhat better addressed. , Notably, Hartwig recently reported a route to 3-arylazetidine-3-carboxylic esters using a Pd-mediated α-arylation protocol …”