Structure-reactivity study of O-tosyl Cinchona alkaloids in their new synthesis and in hydrolysis to 9-epibases : unexpected formation of cinchonicine enol tosylate accelerated by microwave activation

New methods for O - tosylation of the natural Cinchona alkaloids have been discovered as a biphasic processes with Bu 3 N as a catalyst. The optimized excess of tosy l chloride , necessary for transformation of each of the four alkaloid s into O - tosy l derivative , decreases in the following order : quinine, quinidine, cinchonidine and cinchonine . The same decreasing order has been noticed for the hy drolysis rate of the appropriate tosylates to 9 - epibases . D iffic ult conversion of O - tosy lcinchonine in the hydrolytic medium of aq ueous tarta ric acid gives 9 - epicinchonine together with parallel formation of cinchonicine enol tosylate. The latter product is obtained as the main when both cinchonine and cinchonidine tosylates react in the presence of salicylic acid under controlled microwave heating . On the basis of X - ray structure of the new alkene product, the stereoselective syn - E2 quinuclidine ring opening process , competing to the S N 2 hydrolysis is postulated for this transformation

Monazite trumps zircon: applying SHRIMP U–Pb geochronology to systematically evaluate emplacement ages of leucocratic, low-temperature granites in a complex Precambrian orogen

Although zircon is the most widely used geochronometer to determine the crystallisation ages of granites, it can be unreliable for low-temperature melts because they may not crystallise new zircon. For leucocratic granites U–Pb zircon dates, therefore, may reflect the ages of the source rocks rather than the igneous crystallisation age. In the Proterozoic Capricorn Orogen of Western Australia, leucocratic granites are associated with several pulses of intracontinental magmatism spanning ~800 million years. In several instances, SHRIMP U–Pb zircon dating of these leucocratic granites either yielded ages that were inconclusive (e.g., multiple concordant ages) or incompatible with other geochronological data. To overcome this we used SHRIMP U–Th–Pb monazite geochronology to obtain igneous crystallisation ages that are consistent with the geological and geochronological framework of the orogen. The U–Th–Pb monazite geochronology has resolved the time interval over which two granitic supersuites were emplaced; a Paleoproterozoic supersuite thought to span ~80 million years was emplaced in less than half that time (1688–1659 Ma) and a small Meso- to Neoproterozoic supersuite considered to have been intruded over ~70 million years was instead assembled over ~130 million years and outlasted associated regional metamorphism by ~100 million years. Both findings have consequences for the duration of associated orogenic events and any estimates for magma generation rates. The monazite geochronology has contributed to a more reliable tectonic history for a complex, long-lived orogen. Our results emphasise the benefit of monazite as a geochronometer for leucocratic granites derived by low-temperature crustal melting and are relevant to other orogens worldwide