Propargylmagnesium Bromide Research Articles

Formal allene insertion into amides. Reaction of propargyl magnesium bromide with morpholine amides

Formal allene insertion into amides. Reaction of propargyl magnesium bromide with morpholine amides

Diastereoselectivity of the Addition of Propargylic Magnesium Reagents to Fluorinated Aromatic Sulfinyl Imines.

The addition of propargylmagnesium bromide to fluorinated aromatic sulfinyl imines gave homopropargyl amines with total regio- and diastereoselection. Complete reversal of diastereoselectivity can be achieved in some cases using coordinating (THF) or noncoordinating (DCM) solvents. Substituted propargylic magnesium reagents have been also tested toward fluorinated aryl sulfinyl imines affording chiral homoallenyl amines with good yields and selectivity control. DFT calculations helped to rationalize the origin of the experimental regio- and diastereoselectivities observed in each case.

Practical Synthesis of 2-Keto-3-deoxy-d-glycero-d-galactononulosonic Acid (KDN)

Reaction of propargylmagnesium bromide with 2,3;5,6-di-O-isopropylidene-D-mannonolactone followed by highly stereoselective reduction of the so-formed lactol with sodium borohydride gives a syn-diol from which practical syntheses of 2-keto-3-deoxy-D-glycero-D-galactononulosonic acid (KDN) and various partially protected derivatives have been achieved all of which feature the oxidative unmasking of the α-keto acid moiety from the alkyne.

A modular, efficient, and stereoselective synthesis of substituted piperidin-4-ols.

A modular, efficient, and stereoselective synthesis of substituted piperidin-4-ols.

ChemInform Abstract: New Intramolecular Five-Endo-Mode Cyclization of Allenyl Aryl Ketones.

A convenient preparation of allenyl aryl ketones was achieved by the Weinreb-modified Grignard reaction of N-methoxy-N-methylamides with propargylmagnesium bromide. On treatment with BF3·OEt2, the ...

ChemInform Abstract: Syntheses of Branched Non‐1‐ynitols by Chemoselective Addition of (Trimethylsilyl)propargylmagnesium Bromide at the Anomeric Center of Side Chain Halogeno Functionalized Carbohydrates.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Syntheses of Branched Non‐1‐ynitols by Chemoselective Addition of (Trimethylsilyl)‐propargylmagnesium Bromide at the Anomeric Center of Side Chain Halogeno Functionalized Carbohydrates

A convenient method for the syntheses of non‐1‐ynitols 8a–8d, by chemoselective addition of (trimethylsilyl)‐propargylmagnesium bromide at the anomeric center of a 1‐unprotected sugar, in the presence of 3‐C′‐halide and 3‐C′‐silyl functions in the side chain is described. In addition, an efficient method for the synthesis of 3‐C′‐hydroxymethyl sugar 3 via the addition of C1 silyl Grignard reagents to ulose 1 and subsequent oxidation by the Fleming‐Tamao method in excellent yields is reported. Also, a suitable acid‐catalyzed isomerization of the 1,2‐O‐isopropylidene group to the 2,3‐O‐isopropylidene group (5a–5f), to get access to the anomeric center, in good to excellent yields has been depicted.

Cyclopolymerization of 1,1-Dipropargyl-1-silacyclohexane by Transition Metal Catalysts

A conjugated spirocyclic polymer was synthesized via the cyclopolymerization of 1,1-dipropargyl-1- silacyclohexane with various transition metal catalysts. The monomer, 1,1-dipropargyl-1-silacyclohexane was synthesized by Grignard reaction of 1,1-dichloro-1-silacyclohexane with propargyl magnesium bromide. This polymerization proceeded well to give the corresponding poly(1,1-dipropargyl-1-silacyclohexane). The catalytic activity of WCl6 was found to be similar with that of MoCl5. The structure of polymer having the conjugated backbone with silacyclohexane moieties was characterized by such instrumental methods as NMR (1H-, 13C-), IR, and UV-visible spectroscopies. The resulting polymers were mostly yellow or light-brown powders, depending on the catalyst systems used. This polymer was completely soluble in halogenated and aromatic hydrocarbons such as chloroform, 1,2-dichloromethane, benzene, toluene, and chlorobenzene, etc. The thermal and oxidative stabilities of polymer were also studied and discussed.

Stereoselective synthesis of trans-fused tetrahydrofuran derivatives of 5 H-dibenzo[ a, d]cycloheptene

The epoxides derived from 5 H-dibenzo[ a, d]cycloheptene and its 2-fluoro derivative were converted to trans-fused hydrofurans 4a, b (55 and 44% overall yields) via a five-step sequence, i.e. (i) epoxide ring opening using propargylmagnesium bromide, (ii) mercury(II)-induced cyclisation and in situ bromination to give the bromomethylene substituted hydrofurans, (iii, iv) acid catalysed hydration and stereoselective reduction of the hemiacetal intermediates, and (v) base promoted cyclisation.

Efficient Asymmetric Synthesis of Pumiliotoxin Cvia Intramolecular [4+2] Cycloaddition

An efficient asymmetric synthesis in nine steps of natural (−)-pumiliotoxin C (1), a decahydroquinoline alkaloid found in the skin of Central American frog species, is presented. The enantiomerically pure starting material (S)-norvalinol (3), obtained from commercial (S)-norvaline, was cyclized in a one-pot procedure to the tosylated aziridine 5. Ring opening with propargylmagnesium bromide led to the acetylenic sulfonamide tosylamide 6, free of the allenic isomer. Compound 6 was methylated on the acetylenic C-atom, reduced, and deprotected with Na in liquid NH3 to give the (E)-configured unsaturated amine 8, which was condensed with crotonaldehyde to the imine 9 and N-acylated with isobutanoyl chloride to the key intermediate 2. Intramolecular Diels-Alder reaction furnished a diastereoisomeric mixture of N-protected octahydroquinolines 10. After catalytic hydrogenation and cleavage of the amide, natural 1 was obtained as the main product in 25% overall yield; 3.2% of its isomer 11 with the inverse configurations in position 4a, 5, and 8a was also isolated.

Synthesis and characterization of stereospecific 1-propargyl-2-(dimethoxymethyl)-1-cyclohexanols.

Stereochemical isomers with hydroxy groups were synthesized by reacting 2-(dimethoxymethyl)cyclohexanone with propargylmagnesium bromide. The stereo chemical structures were identified by NMR spectral interpretation and the geometry optimization. To assist the NMR interpretation, geometry optimization based on semi-empirical AM1 and PM3 methods was applied. Throughout this study, the structures of the two isomers were all determined and 1H and 13C NMR spectra were fully assigned. It was proven that the less polar isomer is an axial alcohol and the more polar one is an equatorial alcohol.

Estramycins: a potential acyclic diyl precursor derived from estradiol

The estradiol derived enyne 2 is obtained via a nine step sequence starting from estrone. Key-steps involve the opening of the α-epoxide 7 and the 1,2-addition of propargylmagnesium bromide on the allene ketone 10. The allylic alcohol 2 possesses the required functionalities for yielding, after dehydratation, the unsaturated core structure that is expected to cycloaromatize via Myers cyclization. So far, however, this elimination reaction has been unsuccessful.

Trimethyl borate induced thermal cycloaromatization of 1-aryl-1-(prop-2-ynyl)-3,3-bis(alkylthio)-2-propen-1-ols through acetylenic oxy-cope rearrangement

The carbinol acetals 2a-h obtained by 1,2-addition of propargylmagnesium bromide to acyclic α-oxoketene dithioacetals 1a-h undergo cycloaromatization in the presence of trimethyl borate/methanol to give 2,5-bis(alkylthio)biphenyls 4a-henic oxy-Cope rearrangement and an unprecedented 1,4-alkylthio shift in the resulting allenic intermediate.

Stereoselective Synthesis of Steroids and Related Compounds, IV. Addition of Cerium Reagents Derived from (Trimethylsilyl)propargyl Bromide to Aldehydes

AbstractThe addition of (trimethylsilyl)propargylmagnesium bromide (9) to aldehydes afforded predominantly the allenylic alcohols rac‐10. The regioselectivity of this addition changes dramatically when organocerium reagents were used for the addition. In this case nearly exclusive formation of the homopropargylic alcohols rac‐8 was observed. Highest selectivity for this process was obtained when cerium(III) isopropoxide (13) was used as a precursor for the formation of the organocerium reagent. magnified image

New Intramolecular Five-Endo-Mode Cyclization of Allenyl Aryl Ketones

Abstract A convenient preparation of allenyl aryl ketones was achieved by the Weinreb-modified Grignard reaction of N-methoxy-N-methylamides with propargylmagnesium bromide. On treatment with BF3·OEt2, the allenyl aryl ketones were converted to methylenebenzocyclopetenones via a new 5-endo-mode cyclization.

A concise synthesis of the methyl esters of (10S)-hepoxilin B3 and (10S)-trioxilin B3

2,3:4,5-Di-O-Isopropylidene-D-mannose was converted to lactol 2,3-O-isopropylidene-6(Z)-dodecene-L-ribofuranose (6) by Grignard addition with propargyl magnesium bromide, alkylation of the resulting terminal alkyne, partial hydrogenation of the triple bond, and finally chemoselective cleavage of the 1,2-O-isopropylidene and subsequent periodate cleavage of the glycol. Wittig olefination of 6 led to methyl 10(S),11(R)-O-isopropylidene-10,11,12(R)-trihydroxyeicosa-5,8,14(Z)-trienoate (5), which could be converted to (10S)-trioxilin B 3 methyl ester (3) in one step or to (10S)-hepoxilin B 3 methyl ester (4) in three steps

Versatile Syntheses of Alkynyl- and Substituted Alkynylcyclopropanes: 2-Alkoxyethynylcyclopropanes for the Anellation of Bicyclo[3.3.0]octane Fragments

Enol ethers 1a-f are brominated at - 78° C and the resulting alkyl 1,2-dibromoethyl ethers are regioselectively coupled with propargyl-magnesium bromide to give 4-alkoxy-5-bromo-1-pentynes 2a-f, which are protected at the acetylenic terminus with a trimethylsilyl group. These 4-alkoxy-5-bromo-1-trimethylsilyl-1-pentynes 3a-f readily cyclize by γ-elimination to give trimethylsilyl protected 2-alkoxyethynylcyclopropanes 4a-f in excellent overall yields. Under appropriate conditions (E)-diastereomers (E)-4a-f can be prepared selectively. The diastereoselectivity of the bromine addition onto enantiomerically pure chiral enol ethers 1e and 1f, however, is 64% (for 2f) at best. 2-Alkoxy-1-trimethylsilylethynyl-cyclopropanes (E/Z)-4 can be deprotonated with LDA or butyllithium to give configurationally stable 1-lithio derivatives (E)-6, which are trapped by reactive electrophiles (protons, carbonyl compounds, tosyl halides) with retention of configuration on the three-membered ring. 2-Alkoxy-1-ethynylcyclopropanes 5 can be used to anellate a bicyclo[3.3.0]octane fragment onto a cycloalkene in a domino-type reaction sequence, as demonstrated by the Pauson-Khand cycloaddition of (E)-5c to norbornene (14) as well as deltacyclene (20), and subsequent interconversion to the tetracyclic and hexacyclic compounds anti/syn-19 and anti/syn-25/27 with a reasonable degree of diastereoselectivity.

1,2,5-Trimethyl-4-allyl(propargyl)-4-aryl(hetaryl)aminopiperidines

Individual geometrical isomers of some 1,2,5-trimethyl-4-allyl-4-aryl(hetaryl)aminopiperidines were isolated, and their structures were established. 1,2,5-Trimethyl-4-propargyl-4-aryl(aralkyl)aminopiperidines were obtained from 1,2,5-trimethyl-4-aryliminopiperidines and propargylmagnesium bromide.

ChemInform Abstract: Aromatic Annelation via α‐Oxoketene Dithioacetals: Synthesis of Thioresorcinol Dimethyl Ethers. Part 56.

AbstractThe α‐oxoketene dithioacetals (I) are coupled with propargylmagnesium bromide (II) to produce the alcohols (III) which are cyclized with boron trifluoride, yielding the 3‐thiomethylanisoles (IV).

Aromatic annelation via ∝-oxoketene dithioacetals:synthesis of thioresorcinol dimethyl ethers

A novel aromatic annelation leading to fused thioresorcinol dimethylethers has been developed by reacting cyclic ∝-oxoketene dithioacetals with propargylmagnesium bromide followed by treatment of the resulting carbinolacetals with borontrifluoride etherate in methanol.