The stereoselective synthesis of the 3-azabicyclo[3.2.0]heptanes 6, 12, 13, 17, 22, 23 and 24 by an intramolecular [2+2]-photocycloaddition is described. The product yield was good to excellent in almost all cases studied (65-87%) except for a single example (21 → 24) in which a low yield was recorded (22%). The facial diastereoselectivity of the reaction is high if a-branched N,Ndiallylamines are employed as starting materials which either bear a comparably bulky a-substituent (25) or the a-substituent of which is connected to the nitrogen atom via an oxazolidinone ring (16, 19, 20, 21). These diallylamines were readily prepared from methionine and it was shown that their preparation proceeded free of racemization. The photocycloaddition could be conducted in two ways. The more general method is based on the Cu-catalyzed reaction which was carried out with Cu(OTf) 2 in diethyl ether and is applicable to essentially all substrates under scrutiny. The N-cinnamyl substituted substrates 5, 11, 16 and 25 which possess a comparably low lying T 1 state reacted well in a triplet-sensitized process employing acetophenone as the sensitizer and acetone as the solvent.
It is well known that, on reduction, TiO forms extended planar defects, known as Crystallographi~ Shear (CS) Planes, ~~at accommodate the non-stoichiometrv. Further, these CS Planes interact over large distances (~lOOA or more) to form regular, or nearly regular arrays in an otherwise perfect crystal. It has been shown, by theoretical computer based atomistic :simulation studies that extensive structural relaxation :around the CS Plane is responsible for its stability ,over point defect formation, even in composition regions ,very close to stoichiometry. 'In this paper, we will elaborate on these earlier findings, and show how our computer simulation studies correctly predict, firstly, the formation of the Magnetic phases, Ti 0 2 _ 4
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