Conformation of thietans

The conformation of thietane-1-oxide (185), determined from its H NMR spectrum taken in a nematic solvent, was found to have the oxygen equatorial and to be strongly puckered with an angle of puckering of about 38°, in agreement with the results of a microwave study170. 

Theoretical analyses of the conformations of thietanes are in agreement with the observed ring-puckering. " More data concerning the conformations of thietanes are derived from dipole moments, and microwave30-41 Raman,and nmr spectroscopy... 

The structures of four-membered rings are of considerable interest, owing in part to the low-frequency ring puckering vibration203. The comparison of the structures and conformational preferences of thietane oxides and dioxides discussed above with those of dithietane oxides and dioxides is therefore appropriate and will follow. 

Sakamoto et al. reported an intramolecular [2+2] thietane formation in the solid state (Scheme 7). [26] Achiral A-(thiobenzoyl)methacrylamide 39 formed (E,Z)-conformation of the imide moiety, crystallized in a chiral space group Phhh, and the photolysis of single homochiral crystals at room temperature resulted in the formation of an optically active thietane-fused 3-lactam (40,75%) with 10% ee. The solid-state photoreaction proceeded even at -45°C to give higher ee value, 40% ee (conv. 30%, yield 70%). 

The S-NTs bond prefers an equatorial conformation. Of cyclic (four-seven-membered rings) and acyclic sulfides, thietane reacted slowest with chloramine-T. The chloramine-T reactions really proceed via an electrophilic attack by chlorine on sulfur. 

Raman spectral-band frequencies for poly (thietane) as a crystallized melt annealed at 62° satisfy the rules for a longitudinal acoustic-mode frequency for deducing thickness. The morphology and physical properties of isoprene thietane block copolymers have been studied. Potential energies have been calculated for helical- and glide-type conformations of poly (thietane), and the conformations of the homopolymer have been calculated. ... 

The structure of thietane 1-oxide has been investigated by microwave spectroscopy dihedral angle 145.1°, C-S, 1.836A C-C, 1.542A C-S-C 75.7°, C-C-C, 95.9° S-C-C, 89.6°. The sulfoxide oxygen prefers the equatorial position. The ring-puckering has also been studied by infrared spectroscopy the barrier to interconversion between a stable equatorial form and an axial conformer is about 3440 cal/mole. ... 

Dipole moments of thietane 1-oxide derivatives have been used to differentiate cis and trans isomers and to indicate a puckered conformation for the... 

Treatment of thietanes with chloramine T gives N-tosylsulfilimines, for example, 126. Acyclic and five-, six-, and seven-membered cyclic sulfides all react more rapidly than thietane. The mechanism has been investigated. The IR stretching vibrations of the S-N-SO2 system are at 948 and 759 cm", and the nmr spectrum of 3,3-dimethylthietane 1-tosylsulfilimine in benzene and chloroform suggests an equatorial conformation for the sulfilimine. Oxidation of this sulfilimine gives the sulfoximine derivative, 127. The two diastereomeric tosyl-sulfilimines of 3-methyl-3-phenylthietane complex at nitrogen with silver ion. ... 

The dipole moment of thietane 1,1-dioxide in benzene solution is 4.49 The dipole moment of 3.33 D for 3-chlorothietane 1,1-dioxide is in better agreement with a planar than a nonplanar ring conformation, The dipole moments of 3-hydroxy-3-methyl-(jU = 4.73 D, dioxane, axial OH), 3,3-dimethyl (jli = 4.56D, CCI4), 3-phenoxy-( u = 4.13 D, CCU), and 2,3-dichloro-4,4-diphenyl (cis, 2a, 3e, /.i = 4.51 D, CeHg trans 2e, 3e, = 3.32 D, thietane 1,1-dioxides have been... 

Aspects of the configuration, conformation, and n.m.r. properties of thietan derivatives are so closely interwoven that they are reviewed... 

The predominant conformation of a thietan ring is normally determined by the propensity of substituents to adopt the equatorial orientation, - so that 3-substituted thietans and c/5-2,4>disubstituted thietans favour the conformations depicted by (100) and (106), respectively. The two equi-energetic conformations (107) and (108) of rra j-2,4-diphenylthietan, and (109) and (110) of rran5 -2,4-dimethylthietan rapidly equilibrate at room temperature. With polar substituents, electrostatic interactions may play a role in determining the preferred conformation, since the favoured conformation of 2,2-diphenyl-cw-3,4-dichlorothietan, according to dipole-moment data, is that with the 3-chlorine equatorial and 2-chlorine axial (111), although steric repulsive non-bonded interactions appear to be less severe in the alternative conformation (112). 2,2-Diphenyl-m-3,4-... 

Reactions.—2,2,4,4-Tetra-acylthietan monoxides are photochemically converted into cyclopropanes.The conformational aspects of thietan monoxides have been assessed, using lanthanide shift reagents and n.m.r. spectroscopy. ... 

Computational studies on two cis and trans conformers of 2,4-diphenyl thietane dioxide, 2,4-diphenyl thietane, 2,4-diphenyl azetidine, and 2,4-diphenyl oxetane indicate that the cis conformers are more stable than trans.The cycloisomerization of a bicy-clo[4.1.0] substrate into 4,5-dihydrobenzo[ ]furan has been investigated by computational methods (Scheme 96). ... 

The H n.m.r. spectrum of thietan 1-oxide at 300 and at 100 MHz indicates a preferred puckered conformation, with the oxygen in an equatorial position. Determinations of the crystal structures of both cis- and rra j-3-/7-bromophenyl-thietan 1-oxide show that the oxygen atom is equatorial in both isomers in the solid state, and further evidence for a puckered conformation has been obtained from microwave spectroscopy. ... 

It is well-documented that the thietane ring is puckered193 and an energy barrier exists to planarity. Hence two conformations must be considered for each isomer of the cis- and... 

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