Franciscus J. J. de Kanter

Olefin cycloadditions of the electrophilic phosphinidene complex iPr2N-P=Fe(CO)4

Highly strained methylenephosphiranes are formed in the reaction of the new electrophilic phosphinidene complex [iPr(2)N-P=Fe(CO)(4)] with allenes. Remarkably, reaction with diallenes at 0 degrees C also leads to a phosphirane, which rearranges upon warming to room temperature to a bis-isopropylidenephospholene (see scheme).

Synthesis and conformational analysis of 68,11-dihalo[5]metacyclophanes

Abstract The synthesis of the 8,ll-dihalo[5]metacyclophanes 1b-1d (halogen = chlorine or bromine) from 1,2-dimethylenecycloheptane ( 2 ) is described. Spin saturation transfer and line shape analysis of the temperature dependent 1H NMR spectra showed 1b-1d to occur in two conformations A (85-89%) and B (15-11%, respectively). The conformation of the pentamethylene bridge was fully analyzed from vicinal proton coupling constants which obey the Karplus relation inspite of severe distortions of the carbon valence angles. The thermodynamic parameters of the ground and transition state were determined for the equilibrium between the conformers A and B and are discussed in terms of steric interactions in these highly strained molecules.

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 .

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.

1,4-Addition of a Terminal Phosphinidene Complex to [5]Metacyclophane

Three novel aspects emerge for the reaction of [5]metacyclophane (1) with the (intermediate) phenylphosphinidene complex 2 to give the 7-phosphanorbornadiene 3. It is the first 1,4-addition of a phosphinidene complex to an unsaturated system, the first addition of a phosphinidene complex to a benzene ring, and the first [4+1] cycloaddition to an aromatic compound.

Mixed tetramers of sec-butyllithium and 3-methoxypropyllithium ; degree of intracluster etheration and reactivity of sec-butyllithium towards ethylene

Abstract In benzene, neither sec -butyllithium ( 1 ) nor 3-methoxypropyllithium ( 2 ) react with ethylene, while in solutions containing 1 plus 2 3-methylpenty- llithium ( 3 ) is produced by ethylenation of 1 . Clusters 1 n 2 4−n (n: 0 – 4) are indicated by NMR and 1 2 2 2 is deduced to be the most reactive species. At [ 2 ]:[ 1 ] = 2, the reaction order in 1 is 0.74, signifying reversible formation of a pre-reaction complex 1 2 2 2 ·ethylene.

3-methylenetetrahydrofurans and 3-methylenepyrrolidines by addition of 2-(bromozincmethyl)-2-alkenyl ethers or 2-(chloromagnesiomethyl)-2-alkenyl ethers to aldehydes, ketones and imines followed by pd(0)-catalyzed cyclization

Abstract Reaction of 2-(bromozincmethyl)-2-alkenyl ethers 1 or 2-(chloromagnesiomethyl)-2-alkenyl ethers 2 with aldehydes, ketones and imines affords the addition products 4 and 8 , which undergo Pd(0)-catalyzed cyclization to the 3-methylenetetrahydrofurans 6 (R 1 = H) and 3-methylenepyrrolidines 10 (R 1 = H). Addition of 1a or 1b to α,β-unsaturated substrates proceeds in the 1,2-mode only. Reaction of the 3-alkyl derivatives 1c,d,e and 2b leads in almost all cases to the branched addition products 4 or 8 . Under the conditions of ring closure, 4 or 8 (M=ZnBr) are unstable and isomerize to the corresponding linear addition products 13 or 17 . With 4 (M = ZnBr), Pd(0)-catalyzed cyclization is faster than isomerization to 13 , thus permitting regiospecific and stereoselective formation of the tetrahydrofurans 6 . In case of 8 (M = ZnBr), however, isomerization to 17 is faster than ring closure and, consequently, Pd(0)-catalyzed cyclization leads to a mixture of cyclization products 10, 19 and 20 . Branched addition products 4 and 8 , derived from magnesium compound 2b , are stable under the conditions of ring closure permitting regiospecific and stereoselective preparation of tetrahydrofurans 6 (R 1 ≠ H) and pyrrolidines 10 (R 1 ≠ H).

Allylmetallation of 1-silylalkynes by 2-(bromozincmethyl)-2-alkenyl ethers followed by Pd(0)-catalyzed cyclization: A one-pot synthesis of 4-methylenecyclopentenes

Abstract Reaction of 2-(bromozincmethyl)-2-alkenyl ethers 1a,b,c,d with 1-(trimethylsilyl)-1-alkynes 2 afforded carbometallation products 3, which were converted by Pd(0)-catalyzed cyclization to 4-methylenecyclopentenes 5. The rates of both the addition and cyclization step depend on the concentration of the organozinc compound and the preparation of 5 is best performed using a 1.4–1.8 M solution of 1. At lower concentrations reaction times must be longer and, when 1c is reacted, the addition is incomplete and gives rise to a mixture of products (3 and 14), which on Pd(0)-treatment leads to a mixture of isomeric methylenecyclopentenes (5, 15 and 16).

Addition of 2-(chloromagnesiomethyl)2-alkenyl ethers to epoxides followed by Pd(0)-catalyzed cyclization: a one-pot synthesis of 3-methylenetetrahydropyrans

Abstract Addition of 2-(chloromagnesiomethyl)-2-propenyl ethers 1a and 1b to epoxides 3 affords ring opening products 6 or 7 which are converted by Pd(0) to 3-methylenetetrahydropyrans 9 . Cyclization of the addition products is best effected by a catalyst system generated in situ from Pd(OAc) 2 and (i-PrO) 3 P.

Asymmetric addition of B-[2-(phenoxymethyl)-2-propenyl]bis(2-isocaranyl)borane to aldehydes and further cyclization to chiral 3-methylenetetrahydrofurans

Allylboration of aldehydes with the functionalized B-allylbis(2-isocaranyl)boranes 3 afforded functionalized homoallyl alcohols 4 with 71–91% e.e.. After deprotonation 4 can be cyclized under Pd(O) catalysis to give chiral 3-methylenetetrahydrofurans 5.