Tautomers ring conformations

Generate stereoisomers (maximum) 132 per ligand Generate low energy ring conformations i per ligand F Desalt F Generate tautomers Output format > Maestro v- SDF... 

Reviews on the following aspects of four-membered heterocycles have appeared 1,2-dioxetans and the reaction of singlet oxygen with alkenes/ /8-lactam antibiotics, small ring compounds of sulphur and selenium," recent developments in the synthesis of azetidines, the chemistry of benzazetes and of thiacyclobutenes (thietes) and their valence tautomers, and conformational barriers and interconversion pathways in some small ring systems. ... 

Schmidt reaction of ketones, 7, 530 from thienylnitrenes, 4, 820 tautomers, 7, 492 thermal reactions, 7, 503 transition metal complexes reactivity, 7, 28 tungsten complexes, 7, 523 UV spectra, 7, 501 X-ray analysis, 7, 494 1 H-Azepines conformation, 7, 492 cycloaddition reactions, 7, 520, 522 dimerization, 7, 508 H NMR, 7, 495 isomerization, 7, 519 metal complexes, 7, 512 photoaddition reactions with oxygen, 7, 523 protonation, 7, 509 ring contractions, 7, 506 sigmatropic rearrangements, 7, 506 stability, 7, 492 N-substituted mass spectra, 7, 501 rearrangements, 7, 504 synthesis, 7, 536-537... 

Some triazepinones in which one of the nitrogen atoms belongs to a fused azole moiety have been reported. For instance, compound 63 was prepared (74JHC751) and its X-ray structure determined (75CSC317). Similarly, and NMR spectra and X-ray structural determination of 64 revealed that this compound exists as a 3//-tautomer with the 1,2,4-triazepine ring in a distorted boat conformation (88T7185). 

Unsymmetrically substituted formazans form a complex mixture of valence tautomers and geometric isomers with different conformations. The tautomerism is further complicated when substituents on the aryl ring are... 

The spontaneous oxepin-benzene oxide isomerization proceeds in accordance with the Woodward-Hoffmann rules of orbital symmetry control and may thus be classified as an allowed thermal disrotatory electrocyclic reaction. A considerable amount of structural information about both oxepin and benzene oxide has been obtained from theoretical calculations using ab initio SCF and semiempirical (MINDO/3) MO calculations (80JA1255). Thus the oxepin ring was predicted to be either a flattened boat structure (MINDO/3) or a planar ring (SCF), indicative of a very low barrier to interconversion between boat conformations. Both methods of calculation indicated that the benzene oxide tautomer... 

Cycloheptatriene 1 and substituted derivatives thereof do not generally contain detectable amounts of their norcaradiene valence tautomers at equilibrium1-2. However, the bicyclic (tropy-lidene-type) adduct is generally not obtained with diazenes, probably due to the decreased reactivity of the boat conformation of cycloheptatriene. Instead, the tricyclic (norcaradiene-type) adduct 2 is obtained with the most reactive diazenes, i.e., 4-phenyl- and 4-methyl-3W-1,2,4-tri-azolc-3,5(4W)-diones. Ene reaction can also compete. The reaction course is affected by the nature of the diazene, the reaction conditions, the substitution pattern and the nature of the substituents on the cycloheptatriene ring. 

It seems necessary to accept an intermediate species with either zwitterionic or closely related character. The most recent proposal [2gg] invokes the known conformational features of the pregnan-20 0ne side-chain (p. 12). The individual steps are considered to be (i) formation of the i7a-bromoenolate anion (21) with the side-chain in its most stable conformation (ii) rotation about the C i7) C(20) bond to minimise dipole interactions between the i7a-Br and 20-oxygen substituents 22 (iii) expulsion of Br , perhaps assisted by the anti-perlplanar -0 entity to give the unsaturated epoxide (23) or its valence tautomer, the zwitterion 24) (iv) cyclopropanone ring closure and (v) base-promoted rupture to give the Favorskii product. 

---