G. W. Klumpp

3-Methylenetetrahydrofurans and 3-methylenepyrrolidines by addition of 2-bromozincmethyl-2-propenyl ethers to aldehydes, ketones and imines followed by pd(O)-catalyzed cyclization

Abstract Reaction of 2-(benzyloxymethyl)- and 2-(phenoxymethyl)allylzinc bromides 1a and 1b with aldehydes, ketones and imines afforded the addition products 3 and 6 , which underwent Pd(O)-catalyzed cyclization to the tetrahydrofurans 4 and pyrrolidines 7 .

Lithiated 2-alkynyl-1,3-dioxanes as fully oxygenated acyl-anion equivalents: synthesis of 1-alkynyl ketones

Abstract 2-Lithio-2-(trimethylsilylethynyl)-1,3-dioxane 3 is prepared from 2-(trimethylsilylethynyl)-1,3-dioxane with n-BuLi. Alkylation of 3 produces propargylic ketals 2 exclusively. Reaction with group IV-B chlorotrimethylimetalanes gives both propargylic products 2 and allenes 6 depending on the solvent used. Desilylation of 2 as well as hydrolysis to the alkynyl ketones 1 can be carried out under mild conditions. The first 1-alkynyl stannyl ketone has been prepared in this way. Formation of 2-lithio-2-(3,3-dimethyl-1-butynyl)-1,3-dioxane 10 requires t-BuLi. With various electrophiles 10 yields propargylic products and/or allenes in ratios depending on the solvent used.

Zur herstellung und reaktivität von bis(trimethylsilyl)dilithiomethan

Abstract At −90°C in THF or similar media bis(trimethylsilyl)dichloromethane 2 reacts with lithium-4,4′-di- tert -butylbiphenyl (LiDBB) or suspensions of freshly sublimed lithium to give the title compound 1 that can bind two equivalents of various electrophiles. 1 has a great propensity for proton abstraction and it is markedly less reactive towards ethyl iodide than (Me 3 Si) 2 EtCLi 6 .

IN SEARCH OF STABLE LITHIUM PENTAORGANYLSILICATES; SPECIAL ROLE OF FIVE PHENYL LIGANDS AND OF LIGANDS CONTAINING THE 1,4-(1,3-BUTADIENEDIYL) UNIT

Abstract Among several tetraorganylsilanes tested, only 4–6, containing the 1,4-(1,3-butadienediyl) unit, have been found to form, by addition of a σ-organolithium, lithium pentaorganylsilicates identifiable by characteristic 29Si-NMR chemical shifts. Lithium silicates formed from 4 are of particular stability (and correspondingly low reactivity) and appear to have trigonal-bipyramidal structures that undergo stereomutation with ΔH≠ ca. 50 kJ/mol, ΔS≠ ca. −20 J/kmol. So far, lithium pentaphenylsilicate (3) is the only other lithium pentaorganylsilicate that could be identified by 29Si-NMR.

Oxygen and nitrogen heterocycles by intramolecular magnesium- and zinc-ene reactions; Methylenecyclopentanes by Pd(0) - catalyzed isomerization of 5-(bromozincmethyl)-3-methyleneoxacycloalkanes

Abstract 2-(Alkenyloxymethyl)-2-propenylzinc bromides 2a - e and 2-(allylmethylaminomethyl)-2-propenylzinc (or magnesium) halides 2g rearrange thermally to 5-(l-bromozincalkyl)-3-methyleneoxacycloalkanes 1a - e and 5-(bromozinc[or chloromagnesium]methyl)-3-methylene- N -methylpiperidine 1g ; some of the former can be isomerized by Pd(PPh 3 ) 4 to methylenecyclopentanes 3 .

7-Lithio-norbornadiene

Abstract A synthesis of the title compound is described as well as its reactions with some electrophiles.

1,5-annelated 4-methylenecyclopentenes by intramolecular type I zinc-ene reactions followed by Pd(0)-catalyzed cyclization

3-(Alk-m-ynyl)-2-(methoxymethyl)-2-propenylzinc bromides 1 (m = 4,5,6) undergo intramolecular carbometallation. The products 2 were converted by Pd(0)-catalyzed cyclization to 1,5-annelated 4-methylenecyclopentenes 3.

REACTIONS OF THE BUTYLLITHIUMS WITH TERTIARY OLIGOETHYLENEPOLYAMINES

Abstract Complexes of t-BuLi monomer with 1,4,7-trimethyl-1,4,7-triazacyclononane (TMTAN, 3-CH 3 ) and tris(N,N-dimethyl-2-aminoethyl)amine ( 4-CH 3 ) were identified by 13 C-NMR. Rapid elimination of LiN(CH 2 CH 2 NMe 2 ) 2 takes place from the free CH 2 CH 2 NMe 2 group of t-BuLi· 4-CH 3 . BuLi complexes of hexamethyltriethylenetetramine ( 5-CH 3 ) and octamethylpentaethylenehexamine ( 6 ) behave similarly, as does 4-CH 2 Li . Complexes of BuLi oligomers are lithiated at free N-CH 3 .

Anionic rearrangements starting with 1-lithio-2-propynyl silyl ethers a route to (β-trimethylsilylvinyl) silyl ketones

Abstract The title compounds undergo silyl-Wittig rearrangement at low temperature and lead to allenolates at room temperature.

Intramolecular zinc-ene reactions of alkynes; preparation of 1,5-annulated 4-methylenecyclopentenes

Abstract Intramolecular Type I zinc-ene reaction of 3-(alk-m-ynyl)-2-(methoxymethyl)-2-propenylzinc bromides 2 (m = 4,5,6) gave five-, six- and seven-membered carbometallation product 3, which on Pd(0)-catalyzed cyclization were converted to 1,5-annulated 4-methylenecyclopentenes 4. Preparation of 4-methylenecyclopentenes by intramolecular Type II zinc-ene reactions of 2-(alk-m-ynyloxymethyl)-2-alkenylzinc bromides 6 (m = 2,3) followed by Pd(0)-catalyzed rearrangement of the carbometallation products 7 is not possible. Addition as well as rearrangement are slow or do not take place.