Conformational studies

Chemical shifts for some representatives of the less common class of A -pyrazolines are shown in Table 13. These cyclic enehydrazines are also probably puckered (69) however, no X-ray determination nor conformational study has been carried out to solve this problem. Compound (70) is representative of the rare N(l)-unsubstituted A -pyrazolines prepared by Burger et al. (79T389). 

The treatment of 3-benzoyl-2-phenylisoxazolidine with strong base generated an aldehyde and a ketimine <74X1121). Under these conditions dimethyl 2-a-methoxyisoxazolidine-3,3-dicarboxylic acid (186) produced isoxazoline-2-carboxylic acid. Reaction of the monomethyl amide (187) gave the corresponding isoxazoline-2-carboxamide (Scheme 60). CD was used in the conformational studies <79X213). 

Conformational study of geissoschizine isomers and their model compounds (geissoschizine is the indolo[2,3-fl]quinolizidine derivative considered to be an important participant of indole alkaloids biogenesis) 99H(51)649. 

Conformational studies of c/5-6,11/)-H- and /rnns-6,ll/)-H-6-methyl-2,3,4,6,7,1 l/)-hexahydro-l//-pyrimido[6,l-n]isoquinolin-2-ones (136 and 137) by means of the MM2 method implemented in the HyperChem 4.5 suggested, that in the lowest-energy conformations heterocyclic moiety adopted trans-fu ed ring annotation in both cases, with a pseudo-equatorial and -axial methyl group, respectively (97LA1165). 

IR data are of no importance for the characterization and structural elucidation of azepines. NMR Spectra and Conformational Studies... 

HNMR spectroscopic studies4 have confirmed that 4-bromo-l//-3-benzazepin-2-amine exists as the 2-amino tautomer and not as the 2-imino-l,5-dihydro form as suggested earlier.42 HNMR spectral data and conformational studies on 17/-l-bcnzazepines,20 and on 1H-, 3H-, and 5/7-2-benzazepinyl phosphonates43 have been published. 

Maser, F., Bode,K., Pillai, V. N. R. and Mutter, M. Conformational Studies on Model Peptides. Their Contribution to Synthetic, Structural and Functional Innovations on Proteins. Vol. 65, pp. 177 — 214. 

Although perhaps not strictly a conformational study, the structure of the gem-disulfoxide 184 was determined by X-ray crystallography169. A comparison of the structural parameters so measured with 1H and 13C NMR chemical shifts led the authors to conclude that chemical shifts should allow configurational assignments to be made to related sulfoxides. 

The previously discussed conformational study of 3-substituted thietane oxides using lanthanide shift reagents185 corroborates the conclusions derived from other NMR studies and suggests that all rrans-3-substituted thietane oxides prefer an equatorial oxygen conformation when the thietane oxides are bound to shift reagents. 

Zamojski A. Chiral (E,E)-l,4-Dialkoxy-l,3-Butadienes. Synthesis, Conformational Studies and Diels-Alder Reactions with Symmetric Dienophiles Chemtracts 2000 13 62-65... 

N-protected aminoacids 14 behave as carboxyl partners in Ag20 promoted reactions of 2-bromo-isobutyramides or -propanamides affording, respectively, esters of 2-hydroxy-isobutyramides (ref. 20a) or lactamides 15 (ref. 20b). While we plan further research on stereochemical and other aspects of these reactions, model units obtained from 2-bromo-isobutyramides have been used in conformational studies of depsi-peptides (ref. 21). 

T. A., Rueter, J.K., and Goodman, M. Synthesis, biological activities, and conformational studies of somatostatin analogues. Tetrahedron 2000, 56, 9819-9831. 

Fig. 2.1 Examples of / -amino acid homopolymers (nylon-3 type polymers) for which conformational studies have been reported...

However, it does not follow that in any individual case, the same applies. The monoketal (6) of the cyclic diketone (5) is much in demand as a synthetic intermediate and in conformational studies. Mono ketalisation is unsatisfactory here - very little of (6) can be isolated. This may be simply because the right conditions have not yet been found. Various solutions to this problem have been published I shall describe two, both based on the statistical method. 

Bicyclic keto ester (22) was needed for conformational studies. The common atoms are marked ( ) and the obvious disconnections of this symmetrical molecule require double alkylation of cyclohexanone with a reagent such as (23), Double 1,5-diCO disconnection of (22) is impossible as you will discover if you attempt it. 

CsHi.Os Y-Hydroxy acid Conformation Study(15) T211... 

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