Michael J. Begley

Procyanidins and polyphenols of Larix gmelini bark

Abstract Methanol extracts of Larix gmelini bark yielded (−)-epiafzelechin, (+)-catechin and (−)-epicatechin, dimeric procyanidins B-1, B-2, B-3 and B-4 and oligomeric procyanidins. Chemical degradation of the oligomers using toluene-α-thiol and acetic acid showed the oligomers to have flavan-3-ol terminal units possessing either the 2,3- trans (catechin) or 2,3- cis (epicatechin) stereochemistry, with the former predominating. Likewise the extension units were shown to consist of flavan-3-ol units with 2,3- trans or 2,3- cis stereochemistry in roughly equal proportion. The average degree of oligomerization was calculated as 6–7 and the number average molecular weight as 1700–2000. The structure of the residual procyanidins remaining in the bark after methanol extraction is also briefly commented upon. Larixinol is shown to have an unusual spirobiflavonoid structure and a pathway of biogenesis is proposed.

The Mössbauer recoil-free fraction and structure : II. Di-μ3-oxo-bis-(μ-dichloro)-bis[μ-dimethyltin(IV)]-bis-[chlorodimethyltin(IV)], and its ethyl homologue

Abstract The crystal structure of the title compound, [ClMe 2 SnOSnMe 2 Cl] 2 , the partial structure of its ethyl homologue, [ClEt 2 SnOSnEt 2 Cl] 2 , and tin-119 Mossbauer data for the two compounds in the temperature range 77–175.5 K are reported. Crystals of [ClMe 2 SnOSnMe 2 Cl] 2 are monoclinic, space group P 2 1/ c , with a 7.258(1), b 18.581(6), c 8.733(8) A, β 109.76(4)°, Z = 4. The structure consists of centrosymmetric dimeric units held in a two-dimensional polymeric lattice by anionic chloride bridges. The central part of the dimeric unit consists of an essentially planar four-membered Me 2 ovbar|SnOSnMe 2 O ring, to the oxygen atoms of which are appended [ClMe 2 Sn] units. The geometries at both endo- and exo-cyclic tin atoms are similar, forming contacts to six neighbouring atoms in a distorted arrangement midway between trigonal bipyramidal and octahedral. Crystals of [ClEt 2 SnOSnEt 2 Cl] 2 are also monoclinic, space group P 2 1/ n , with a 10.3712(4), b 9.4699(6), c 15.9432(1) A, β 106.43(3)°, Z = 4, but the structure has only been partly solved due to disorder. The major component of the disorder (∼75%) has a structure similar to that of [ClMe 2 SnOSnMe 2 Cl] 2 . The second component is best described as a series of alternating [R 4 Sn 2 O 2 ] and [R 2 SnX 2 ] units, in which two of the latter units chelate [Sn 2 O 2 ] four-membered rings. Tin-119 Mossbauer isomer shift, quadrupole splitting, and recoil-free fraction temperature dependence have also been studied and correlated with the crystallographic data. The variation of the recoil-free fraction of [Me 4 Sn 2 Cl 2 O] 2 varies linearly with temperature in the range 77–175.5 K with a temperature coefficient of −1.26 × 10 −2 K −1 . In contrast, the ethyl compound exhibits a discontinuity at ca. 110 K, attributed to a phase change involving a relaxation of the coordination about one of the two crystallographically independent tin atoms.

Simple synthesis of a C2 symmetric vicinal diamine: Highly diastereoselective Grignard addition to a chiral bis-imine

Abstract The reaction of the enantiomerically pure bis -imine derived from glyoxal and ( R )-α-methylbenzylamine with PhMgCl in diethylether is highly diastereoselective, resulting in the selective formation of the C 2 symmetric vicinal diamine 7 .

Phenylantimony(III) diorganophosphorodithioates: the crystal structure of diphenylantimony(III) di-isopropylphosphorodithioate, Ph2SbS2P(OiPr)2; unusual polymerisation through semibonding

Abstract The diphenylantimony(III)phosphorodithioates, Ph 2 SbS 2 P(OR) 2 where R = Me, Et, i Pr and Ph, have been prepared and the methyl and isopropyl derivatives obtained as crystalline solids. The compounds have been characterised by infrared and NMR spectroscopy. An X-ray structural determination for the isopropyl compound shows the presence of two independent molecules in the asymmetric unit, with similar but not identical molecular parameters. The ligand in each molecule is strongly bonded to antimony by one sulphur atom (SbS 2.54 A), but there are two weaker SbS contacts ( ca. 3.2 and 3.8 A) making the ligand effectively tridentate. These interactions generate infinite chains in the solid state, providing an example of a new dithiophosphate structure.

The caffeine—potassium chlorogenate molecular complex

Abstract The crystal structure of the caffeine—potassium chlorogenate 1:1 molecular complex derived from coffee beans is described. The relationship of this structure to the general question of the mechanisms of polyphenol association and precipitation is commented upon.

Polyphenol–caffeine complexation

Crystal structures of complexes of caffeine (1) with methyl gallate (2), m-nitrobenzoic acid (3), and potassium chlorogenate (4) are described; the results are used to comment on possible modes of association of natural polyphenols with substrates such as proteins.

Discrete dinuclear and polymeric copper(I) cations bridged by 4,4′-bipyridine, trans-1,2-bis(4-pyridyl)ethene or bis(4-pyridyl) disulfide

Treatment of an acetonitrile solution of copper(I) tetrafluoroborate and 4,4′-bipyridine (4,4′-bipy) with 2-cyanoguanidine (cnge) yielded [{Cu(cnge)2}2(µ-4,4′-bipy)][BF4]2·MeCN 1. Structural analysis revealed a planar dinuclear cation containing two, three-co-ordinate T-shaped copper centres bridged by 4,4′-bipy and terminally co-ordinated by two cnge molecules. In the absence of cnge but with an excess of copper(I), the product was [Cu(4,4′-bipy)(MeCN)2]BF42, structural analysis of which revealed a one-dimensional polymeric cationic zigzag chain, based on tetrahedral copper(I) atoms bridged by 4,4′-bipy and terminally co-ordinated by two MeCN molecules. The same reaction mixture but with an excess of 4,4′-bipy gave [Cu(4,4′-bipy)2]BF4·MeCN 3. The corresponding trans-1,2-bis(4-pyridyl)ethene (bpe) systems yielded the analogous [{Cu(cnge)2}2(µ-bpe)][BF4]2·6MeCN 4, [Cu(bpe)(MeCN)2]BF45 and [Cu(bpe)2]BF46, respectively. Only one product has been isolated from the corresponding bis(4-pyridyl) disulfide (bpds) systems, [Cu(bpds)(MeCN)2]BF47. Attempts to produce copper(I) derivatives of 3,6-bis(imidazolyl)pyridazine (bimpydz) were unsuccessful, the copper(II) product, Cu(bimpydz)(MeCN)2(BF4)28, invariably being formed. Whereas the [{Cu(cnge)2}2(diimine)]2+ and [Cu(diimine)(MeCN)2]+ cations reacted with NOBF4 and NBut4NO2 forming copper(II) oxidation products, the [Cu(diimine)2]+ cations were unreactive.

Synthesis of spiroethers using radical cyclisations

Abstract A variety of spiroether products, including one bis-spiro compound, are available via a simple radical cyclisation route.

Revised structures for guaianolide α-methylenebutyro-lactones from feverfew

Abstract The structures of two series of guaianolides present in feverfew, Tanacetum parthenium , are established as tanaparthin-α-peroxide, canin and seco -tanapartholide-A [major group] and the corresponding ‘β’-series [β-peroxide, artecanin and the seco -B derivative] using a combination of spectroscopic and X-ray crystallographic analyses and chemical transformations.

Total synthesis of verticillene. A biomimetic approach to the taxane family of alkaloids

Abstract Intramolecular reductive coupling of the bis -aldehyde (10) in the presence of Ti(O), followed by 1,4-reducdon of the resulting tetraene (9) using sodium in ammonia, provides a facile synthesis of E , E -verticillene (8), the putative biogenetic precursor of the taxane family of alkaloids e.g. (1) and (2). Treatment of either verticillene (8), verticillene 7,8-epoxide (21), verticillol 7,8-epoxide (27) or anhydroverticillol 7,8-epoxide (29) with Lewis acids fails to produce the corresponding taxane carbon framework, viz (3), and instead only products e.g. (23), (24) and (31) resulting from rearrangements of the epoxide rings in the substrates are obtained.