Synthesis of Halogenated α,β-Unsaturated γ-Butyrolactone Derivatives by Triphenylphosphine-Catalyzed Cyclization of α-Halogeno Ketones with Dialkyl Acetylenedicarboxylates (=Dialkyl But-2-ynedioates) (original) (raw)
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Utility of α,β-Unsaturated Ketones as Versatile Reagents in Organic Synthesis
Química Nova
The synthetic utility of α,β-unsaturated ketones is reported in a formal way. The title compounds are used as precursors for the synthesis of many heterocyclic rings. The reactions of the title compounds are subdivided in groups that cover reactions to yield monoheterocycles e.g., thiophenes, imidazolidines, pyrimidines, pyridines, pyrazoles and even fused heterocyclic e.g., pyrroloimidazoles, pyrazolopyridines and imidazopyridines.
Tetrahedron Letters, 2009
The enolates formed from Lewis acid treatment of (2-trimethylsilylmethyl)cyclopropyl alkyl and aryl ketones reacted with aldehydes formed in situ from alkoxy-, aryl-and vinyl-substituted oxiranes to generate aldol products in good yields. Selected aldol products were conveniently transformed into highly substituted tetrahydrofurans under oxidative conditions. The ring strain present in a three-membered ring makes it a useful synthon in organic synthesis. Vicinal placement of a donor and an acceptor group on the ring provides dual activation that renders the cleavage of the in-between r C-C bond feasible under mild Lewis acid conditions. A silylmethyl group acts as a donor group for the b-effect of silicon. We have previously reported reactions of enolates generated from the ring cleavage of 2-trimethylsilylmethylcyclopropyl alkyl/aryl ketones with aldehydes, ketones and imines to deliver aldol and iminoaldol products that were subsequently transformed into tetrahydofurans and pyrrolidines, respectively, under oxidative conditions. 2 As an extension of this protocol, we envisioned reactions of 2trimethylsilylmethylcyclopropyl ketones with aldehydes formed in situ from oxiranes to generate aldols in a single step. Application of oxiranes as in situ precursors to aldehydes appeared appealing because (a) generation of oxiranes from alkenes is simple and (b) alkenes bearing diverse substituents are readily available by following literature methods. We report herein the construction of tetrahydrofuran skeleton through the addition of a cyclopropane-derived enolate to an in situ oxirane-derived aldehyde followed by ring closure under oxidative conditions. The resultant 2-hydroxymethyltetrahydrofuran constitutes a common structural feature present in acetogenins that have desirable biological properties such as antineoplastic and immunosuppressive activities. The rearrangement of oxiranes to aldehydes in the presence of Lewis acids is known. We commenced our studies with the screening of Lewis acids for the reaction of an isomeric mixture of 1a with the oxirane 2a (Ar = C 6 H 5 , R = CH 2 OBn). TiCl 4 (1.2 equiv, CH 2 Cl 2 , À78°C), Et 2 AlCl (1.2 equiv, CH 2 Cl 2 , À30°C), LiClO 4 in CH 3 NO 2 (3 equiv, 0.25 M, 25°C), ZnCl 2 (1.5 equiv, CH 2 Cl 2 , 25°C), InCl 3 (1.2 equiv, CH 2 Cl 2 , 25°C), SnCl 4 (1.2 equiv, CH 2 Cl 2 , À78°C), Yb(OTf) 3 (5 mol %, CH 2 Cl 2 , 25°C) and Zn(OTf) 2 (5 mol %, CH 2 Cl 2 , 0?25°C) were unsatisfactory. These reactions were either complicated, leading to the formation of several products, or did not occur at all. In some instances, the cyclopropane had simply transformed into 3-butenyl phenyl ketone, 4, and the oxirane had rearranged to a-benzyloxymethyl-a-phenylacetaldehyde, 5, quantitatively.
Butadienyl Ketene: An Unexplored Intermediate in Organic Synthesis
SynOpen, 2024
Butadienyl ketene is a useful intermediate because of its role as a 2p-component in cycloaddition reactions with a variety of substrates such as simple or conjugated imines and dienes. This review article summarizes recent reports on the generation of butadienyl ketene in situ and their cycloaddition reactions to afford heterocyclic systems. The chemistry of butadienyl ketene is explored with a focus on its [2+2] and [4+2] cycloaddition reactions with a variety of imines and azadiene derivatives such as 1,3-diazabuta-1,3-dienes, for the synthesis of fourand six-membered heterocycles, respectively.
ChemInform, 2005
Pyridine derivatives R 0380 Bis(trimethylsilyl)ketene Acetals as C,O-Dinucleophiles: One-Pot Formation of Polycyclic γand δ-Lactones from Pyridines and Pyrazines.-The reactions of bis(trimethylsilyl)ketene acetals with pyridines, quinolines and isoquinolines in the presence of methyl chloroformate gives the corresponding carboxylic acid substituted heterocycles in satisfactory yields. The isolated acids react with peracids to give β-hydroxy-δ-lactones like (V) and (XIV). The behavior of pyrazines is peculiar, since methyl chloroformate on its own induces the formation of γ-lactones.-(RUDLER*,
Formation and NMR study of some cyclic β-ketodithioacetals
Tetrahedron, 1988
An efficient method has been found for the preparation of cyclic monodfthioacetals of 1,3-dfcarbonyl compounds using boron trffluoride etherate as the acid catalyst. Asynmmtric 1.3-diketones nact r7g ioselectively in most of the cases tried. A study of the C and H nmr characteristics of these compounds has been carried out. The monodithioacetals of 1,3-diketones are potentially useful compounds in synthesis since they are masked 1,3-dioxygen substituted moieties which can be selectively functionalized. Hence, it is possible to perform chain extension reactions as would be necessary in the synthesis of units of the polyol macrolides. Dithioacetals are stable under normal Bronsted acid conditions, hence, allowing much more flexibility in the reaction conditions subsequently used than would be possible for normal acetals. Efficient methods are now known for the reformation of a carbonyl group from 1,3-dfthiolanes and 1.3-dithianesl.