title: Cleavage of Ge–S and C–H bonds in the reaction of electron-deficient [Os₃(CO)₈(μ-H)(μ₃-Ph₂PCH₂P(Ph)C₆H₄)] with Ph₃GeSPh: Generation of thiophenol derivatives [Os₃(CO)₈(μ-H)(μ-SPh)(μ-dppm)] and [Os₃(CO)₇(μ-H)(μ-SPh)(μ₃-SC₆H₄)(μ-dppm)]

authors: Raha, Arun K.

subjects: triosmium clusters

abstract: Heating the electron-deficient [Os₃(CO)₈(μ-H)(μ₃-Ph₂PCH₂P(Ph)C₆H₄)] (1) and Ph₃GeSPh in benzene at 80 °C led to the thiolato bridged compounds, [Os₃(CO)₈(μ-H)(μ-SPh)(μ-dppm)] (2) and [Os₃(CO)₇(μ-H)(μ-SPh)(μ₃-SC₆H₄)(μ-dppm)] (3), formed by cleavage of Ge–S and C–S bonds of the ligand, in 40% and 17% yields, respectively. Both compounds 2 and 3 have been characterized by a combination of elemental analysis, infrared and ¹H NMR spectroscopic data together with single crystal X-ray crystallography. Compound 3 contains an open triangle of osmium atoms bridged by a SPh and SC₆H₄ ligands on opposite sides of the cluster with a dppm ligand bridging one of the Os–Os edges. Compound 2 consists of a closed triangular cluster of osmium atoms with a bridging SPh, and a bridging hydride ligand on the same Os–Os edge, and a dppm ligand bridging one of the remaining Os–Os edges.

text: Cleavage of Ge–S and C–H bonds in the reaction of electron-deficient [Os₃(CO)₈(μ-H)(μ₃-Ph₂PCH₂P(Ph)C₆H₄)] with Ph₃GeSPh: Generation of thiophenol derivatives [Os₃(CO)₈(μ-H)(μ-SPh)(μ-dppm)] and [Os₃(CO)₇(μ-H)(μ-SPh)(μ₃-SC₆H₄)(μ-dppm)] Heating the electron-deficient [Os₃(CO)₈(μ-H)(μ₃-Ph₂PCH₂P(Ph)C₆H₄)] (1) and Ph₃GeSPh in benzene at 80 °C led to the thiolato bridged compounds, [Os₃(CO)₈(μ-H)(μ-SPh)(μ-dppm)] (2) and [Os₃(CO)₇(μ-H)(μ-SPh)(μ₃-SC₆H₄)(μ-dppm)] (3), formed by cleavage of Ge–S and C–S bonds of the ligand, in 40% and 17% yields, respectively. Both compounds 2 and 3 have been characterized by a combination of elemental analysis, infrared and ¹H NMR spectroscopic data together with single crystal X-ray crystallography. Compound 3 contains an open triangle of osmium atoms bridged by a SPh and SC₆H₄ ligands on opposite sides of the cluster with a dppm ligand bridging one of the Os–Os edges. Compound 2 consists of a closed triangular cluster of osmium atoms with a bridging SPh, and a bridging hydride ligand on the same Os–Os edge, and a dppm ligand bridging one of the remaining Os–Os edges.

year: 2008

title: Structural characterisation and absolute stereochemistry of some degraded carotenoids from New Zealand honeys

authors: Broom, Susan J.

abstract: The structures and absolute stereochemistries of some degraded carotenoids from New Zealand native honeys were elucidated. 

Determination of the absolute stereochemistry of 3,5,6-trihydroxy-β-ionone was attempted by an enantioselective synthesis. A racemic synthesis was achieved starting from β-ionone. The key steps involved regioselective hydroboration of 3,4-dehydro-β-ionone, followed by molybdenum-mediated stereoselective epoxidation of the resulting homoallylic alcohol. Ring opening of the epoxide afforded the required trihydroxy-ionone. Synthesis of both enantiomers of 3,5,6-trihydroxy-β-ionone via enantio- and regioselective functionalisation of 3,4-dehydro-β-ionone was not achieved. Methods of enantioselective enzyme-mediated kinetic resolution of cyclic homoallylic alcohols were investigated. A satisfactory procedure was not developed. 

The absolute stereochemistry of 3,5,6-trihydroxy-β-ionone was determined by analysis of the diastereoisomeric proton chemical shifts of (S)- and (R)-α-methoxyphenylacetate (MPA) derivatives using the extended Mosher-Trost configurational model. This analysis indicated a 3S,5R,6R absolute configuration, the same configuration as 3,5,6-trihydroxy carotenoids. The natural product was extracted from thyme (Thymus vulgaris) honey using established procedures.

Diethyl ether extracts of kamahi (Weinmannia racemosa) honey were found to contain three diastereoisomers (kamahines) of an unusual degraded carotenoid with a 14 carbon skeleton. After acetylation, one of the isomers was fully characterised by multidimensional ¹H and ¹³C NMR spectroscopy, and single-crystal X-ray crystallography, indicating the parent alcohol was 4,5-dihydro-1',5-dihydroxy-2',4,8',8'-tetramethylspiro[furan-2(3)H,7'[6']oxabicylco[3.2.1]oct[2']ene]-4'-one. Comparison of NMR-derived NOE and coupling constant data of kamahine A and B acetates with kamahine C acetate indicated the parent kamahines were C-4, C-5 epimers.
 
The absolute configurations of the kamahines were determined by NMR and a molecular modeling study (MacroModel) of the diastereoisomeric hemiacetal MPA esters. The results of the determination, coupled with a consideration of crystallographically-determined hemiacetal ester conformations obtained from a search of the Cambridge Structural Database, supported the use of the Mosher-Trost model for determination of the absolute configurations of hemiacetals. Furthermore, this analysis suggested that the Mosher-Trost model should be amended to take into account a torsion angle of +25-50° between the methine proton and the carbonyl of hemiacetal MPA esters. Kamahines A-C were shown to have the absolute configurations 1'R,2R,4R,5S,5'S, 1'R,2R,4S,5S,5'S and 1'R,2R,4R,5R,5'S, respectively. The absolute configurations of kamahines A-C were consistent with an abscisic acid precursor.

text: Structural characterisation and absolute stereochemistry of some degraded carotenoids from New Zealand honeys The structures and absolute stereochemistries of some degraded carotenoids from New Zealand native honeys were elucidated. 

Determination of the absolute stereochemistry of 3,5,6-trihydroxy-β-ionone was attempted by an enantioselective synthesis. A racemic synthesis was achieved starting from β-ionone. The key steps involved regioselective hydroboration of 3,4-dehydro-β-ionone, followed by molybdenum-mediated stereoselective epoxidation of the resulting homoallylic alcohol. Ring opening of the epoxide afforded the required trihydroxy-ionone. Synthesis of both enantiomers of 3,5,6-trihydroxy-β-ionone via enantio- and regioselective functionalisation of 3,4-dehydro-β-ionone was not achieved. Methods of enantioselective enzyme-mediated kinetic resolution of cyclic homoallylic alcohols were investigated. A satisfactory procedure was not developed. 

The absolute stereochemistry of 3,5,6-trihydroxy-β-ionone was determined by analysis of the diastereoisomeric proton chemical shifts of (S)- and (R)-α-methoxyphenylacetate (MPA) derivatives using the extended Mosher-Trost configurational model. This analysis indicated a 3S,5R,6R absolute configuration, the same configuration as 3,5,6-trihydroxy carotenoids. The natural product was extracted from thyme (Thymus vulgaris) honey using established procedures.

Diethyl ether extracts of kamahi (Weinmannia racemosa) honey were found to contain three diastereoisomers (kamahines) of an unusual degraded carotenoid with a 14 carbon skeleton. After acetylation, one of the isomers was fully characterised by multidimensional ¹H and ¹³C NMR spectroscopy, and single-crystal X-ray crystallography, indicating the parent alcohol was 4,5-dihydro-1',5-dihydroxy-2',4,8',8'-tetramethylspiro[furan-2(3)H,7'[6']oxabicylco[3.2.1]oct[2']ene]-4'-one. Comparison of NMR-derived NOE and coupling constant data of kamahine A and B acetates with kamahine C acetate indicated the parent kamahines were C-4, C-5 epimers.
 
The absolute configurations of the kamahines were determined by NMR and a molecular modeling study (MacroModel) of the diastereoisomeric hemiacetal MPA esters. The results of the determination, coupled with a consideration of crystallographically-determined hemiacetal ester conformations obtained from a search of the Cambridge Structural Database, supported the use of the Mosher-Trost model for determination of the absolute configurations of hemiacetals. Furthermore, this analysis suggested that the Mosher-Trost model should be amended to take into account a torsion angle of +25-50° between the methine proton and the carbonyl of hemiacetal MPA esters. Kamahines A-C were shown to have the absolute configurations 1'R,2R,4R,5S,5'S, 1'R,2R,4S,5S,5'S and 1'R,2R,4R,5R,5'S, respectively. The absolute configurations of kamahines A-C were consistent with an abscisic acid precursor.

year: 1998

title: The chronology of Waikato pā: A spatio-temporal investigation of pā in the middle Waikato basin

authors: McBride, Rowan

subjects: pā

abstract: This study considers the chronology of pā construction, proliferation, and development within the 
Middle Waikato Basin through a spatio-temporal investigation of palisade construction activity as 
identified at six pā (fortified places). The chronological approach applied in this thesis uses 14C 
wiggle-match dating to provide an accurate and precise calendar date for the felling of a tree 
(Felling Date) used to construct a palisade defence at a pā. These Felling Dates are interpreted using 
the theory of time perspectivism, focusing on three distinct scales of analysis: Event, Local, and 
Regional. The event scale of analysis successfully produced twenty high-precision felling dates on 
posts recovered from Lake Mangakaware 1 (MA1), Lake Mangakaware 2 (MA2), Lake Mangahia 
(MGA), Taraheke Pā (TAR), Te Uapata Pā (TEU) and Lake Rotokauri (ROT). The local scale 
analysis utilised these felling dates to track the development of the identified palisade defences 
over time, identifying multiple palisade construction phases, representing construction, repair and 
redevelopment episodes at MA1, MA2, MGA, TAR and TEU. Finally, the regional scale analysis 
integrated this evidence into a broader chronological framework, identifying shared episodes of 
palisade construction activity within the Middle Waikato Basin. This analysis highlights three 
critical periods of proposed socio-political stress and stability between the late fifteenth and early 
nineteenth centuries, related to hypothesised influential variables from the broader cultural and 
archaeological landscape that are proposed to be responsible for the emergence, proliferation and 
development of pā over time.

text: The chronology of Waikato pā: A spatio-temporal investigation of pā in the middle Waikato basin This study considers the chronology of pā construction, proliferation, and development within the 
Middle Waikato Basin through a spatio-temporal investigation of palisade construction activity as 
identified at six pā (fortified places). The chronological approach applied in this thesis uses 14C 
wiggle-match dating to provide an accurate and precise calendar date for the felling of a tree 
(Felling Date) used to construct a palisade defence at a pā. These Felling Dates are interpreted using 
the theory of time perspectivism, focusing on three distinct scales of analysis: Event, Local, and 
Regional. The event scale of analysis successfully produced twenty high-precision felling dates on 
posts recovered from Lake Mangakaware 1 (MA1), Lake Mangakaware 2 (MA2), Lake Mangahia 
(MGA), Taraheke Pā (TAR), Te Uapata Pā (TEU) and Lake Rotokauri (ROT). The local scale 
analysis utilised these felling dates to track the development of the identified palisade defences 
over time, identifying multiple palisade construction phases, representing construction, repair and 
redevelopment episodes at MA1, MA2, MGA, TAR and TEU. Finally, the regional scale analysis 
integrated this evidence into a broader chronological framework, identifying shared episodes of 
palisade construction activity within the Middle Waikato Basin. This analysis highlights three 
critical periods of proposed socio-political stress and stability between the late fifteenth and early 
nineteenth centuries, related to hypothesised influential variables from the broader cultural and 
archaeological landscape that are proposed to be responsible for the emergence, proliferation and 
development of pā over time.

year: 2024