Regioselective Preparation of 2,4-, 3,4-, and 2,3,4-Substituted Furan Rings. 2.1 Regioselective Lithiation of 2-Silylated-3-substituted Furan Rings

Lithium furyl and pyridyl amidinates as building blocks in coordination polymers, ladder and cage structures

Lithium N,N'-bis(trimethylsilyl)heterocyclic amidinate complexes with 3- and 4-pyridyl and 3-furyl carbon substituents were prepared by addition of the corresponding nitriles to LiN(SiMe(3))(2) (LiNTMS(2)) solution. In the presence of N,N,N',N' tetramethylethylene diamine (TMEDA), both pyridyl amidinates crystallize as coordination polymers with an amidinate-Li-pyridyl backbone. The 4-pyridyl derivative (7) creates a linear polymer with amidinate-Li-TMEDA units as side chains, whereas the 3-pyridyl polymer (6) has a two-dimensional (2D) network structure in which TMEDA serves as a cross-linker. Solvation of the reaction mixture of 3-furonitrile and LiNTMS(2) with TMEDA affords the monomeric 3-furyl amidinate Li TMEDA complex (3). Crystals of the Li(2)O complex {[3-furyl-C-(NTMS)(2)Li](4).Li(2)O}.C(7)H(8) (4) are obtained from toluene by partial hydrolysis of the unsolvated 3-furyl amidinate (2). Degradation of the polymer (7) to monomeric units can be achieved by solvation in toluene or by reaction with TMS(2)NLi.TMEDA that affords crystals of the complex {NTMS(2)Li.[4-C(5)H(4)N-C(NTMS)(2)Li.TMEDA]}(2).(NTMS(2)Li.TMEDA) (8). The formation of these aggregates can be rationalized by directed substitution of TMEDA with pyridyl moieties and by the laddering principle.

A new route to furanoeremophilane sesquiterpenoids. Synthesis of (±)-6β-hydroxyeuryopsin

The naturally occurring furanoeremophilane 6[small beta]-hydroxyeuryopsin was synthesized by a novel route which involved Stille coupling of a 2-furylstannane with a cyclohexylmethyl bromide, followed by intramolecular formylation of the furan to complete the tricyclic nucleus of the sesquiterpenoid.

Teubrevin G and teubrevin H: the first total syntheses of rearranged neo-clerodanes including solutions to the problems of chirality merger and furan ring assembly

Total syntheses of teubrevins G (2) and H (3) are described. The reported strategy relies on a highly regioselective cycloaddition-fragmentation approach to the construction of a 2,3,4-trisubstituted furan and features efficient ring-closing metathesis chemistry made possible through the application of a 1,3-dimesityl-4,5-dihydroimidazol-2-ylideneruthenium precatalyst. The key building blocks 39 and 48 were constructed by asymmetric processes and coupled under conditions where good remote asymmetric induction was realized. The diastereoselection observed in this alkylation reaction appears to be intimately associated with the conformational properties of the beta-keto ester enolate. While the readily separated major diastereomer was transformed via a short route to 2, the minor component served as the precursor to 3. The efficiency of the synthesis was thereby well served.

Preparation of 2-Cyanobenzoic Acids from the Reaction of Bromobenzoic Acids with Arylacetonitriles and LDA

The reaction of various bromobenzoic acids 1 with arylacetonitriles 3 in the presence of LDA at -70 degrees C gave predominantly 2-cyanobenzoic acids 4 plus minor amounts of 3-(arylcyanomethyl)benzoic acids 5 and debrominated benzoic acids 6. The reaction is thought to proceed through a benzyne-3-carboxylate intermediate 2, which is formed at -70 degrees C upon the addition of the arylacetonitrile 3 to a solution of the appropriate lithium halobenzoate and excess LDA. The base-initiated generation of an aryne intermediate from a haloarene at such low temperatures is unprecedented. To confirm the orientation of the cyano and carboxylic acid groups, 4-methoxy-2-cyanobenzoic acid (4f) was converted to the corresponding anhydride (8) via phthalic acid (7) and to 3,3-dimethyl- and 3,3-di-n-butyl-2,3-dihydro-5-methoxy-4-(4-methoxyphenyl)-methyl-1H-isoindol-1-ones (9).