Oxetanes and thietanes

The regiospecific carbonylation of oxetanes and thietanes, resulting in a ring expansion... 

The use of high pressure in the synthesis of oxetanes and thietanes is reviewed (92PJC1535) and aspects of oxetane chemistry are discussed (94MI23). 

Ab initio one-electron property calculations. II Molecular oxetane, cyclobutanone, and thietane. °... 

Four-bond 1H,1H coupling constants are useful for the differentiation of diastereomers as their signs are connected to the orientation of the coupling partners if the latter are cis, 4/h.h >s positive, and vice versa467. This rule also holds for thietane dioxides, but there are exceptions in the oxetane and azetidine series (vide infra). 

The PE spectra of several oxetanes and related small ring compounds have received careful study. The first ionization potential for oxetane occurs at 7.65 eV as a sharp, adiabatic transition. This is at significantly lower potential than for oxirane (10.57 eV) or for acyclic ethers (dimethyl ether, 10.04 eV), showing the potential-lowering effect of the four-membered ring. This is seen also in azetidines and thietanes. 

In the present review the ring systems containing one heteroatom are considered first, except for P-lactams which are given a special section at the end. Interest in azetidines continues to be stimulated by the discovery of the potentially useful trinitro derivative. The requirements for the stereoselective synthesis of substituted oxetane are being explored and derivatives of aluminium are useful in the stereoselective routes to oxetanones. The preparation and subsequent pyrolysis of oxetanones is suggested as an alternative to the Wittig route to olefins. Stereoselective routes to thietanes and thietane 1 -oxides are mentioned. 

Microwave spectra have been used to determine molecular dimensions for, inter alia, aziridines and 1-azirines , diazirine and substituted derivatives , diazetidines , oxetanes , and thietanes and thietes . 

The simplest systems involve copolymerization of structurally related pairs of comonomers, polymerizing irreversibly. Copolymerization of different oxetanes [294], thietanes [295], azetidines [296], and oxazolines [297] was studied, the results were interpreted in terms of simple four-parameter copolymerization scheme and the corresponding reactivity ratios for some systems were determined. 

The H nmr spectrum of thietane 1,1-dioxide in a nematic solvent indicates the ring is nearly planar with a very low barrier to planarity, a result that agrees with variable temperature investigations at 300 and 100MHz. An early nmr study compared the chemical shifts of thietane, thietane 1,1-dioxide, oxetane, and cyclobutane. The chemical shift (6) for the a-protons is 4.09 and for the /3-protons, 2.14. The geminal coupling constant for the a-protons is — 14.0 Hz and for the /3-protons, —12.6 Hz. Other coupling constants are /cis 10-3 Hz, Jtmns ... 

Chemistry of azetidin-3-ones, oxetan-3-ones, and thietan-3-ones 02CRV29. Formation of four-membered heterocycles through electrophilic heteroatom cyclization 02EJ03099. 

Four-membered heterocycles include oxetane, 2//-oxete, thietane, 2Ff-thiete, azetidine, and azete. In the field of drug discovery, oxetanes and azetidines are more and more incorporated into drugs for modulating biological and physical properties as well as for expanding intellectual properties space. 

The formation of thietanes from thiones and olefins has been less exploited for synthetic purposes than the corresponding oxetane-forming reaction. It should be remarked that thiocarbonyl compounds very often undergo efficient photoreactions from the second excited singlet state S2 U4). One interesting synthetic application is found in the photochemical preparation of quinolines from N-thioamides (4.84)498). The primary photochemical step is assumed to be the intramolecular thietane formation. 

A. Roy, B. Achari, and S. B. Mandal, An easy access to spiroannulated glyco-oxetane, -thietane and -azetane rings Synthesis of spironucleosides, Tetrahedron Lett., 47 (2006) 3875—3879. 

Photocycloaddition of thiones to alkenes is the most popular and fruitful method for the preparation of the thietane system. In analogy to the formation of the oxetanes by cycloaddition of the electronic excited ( ,tc ) carbonyls, thietanes can be expected to arise photochemically from aromatic thioketones and substituted olefins as well as 1,2- and 1,3-dienes. ° Thiobenzophenone serves as a source of a sulfur atom and, because of its blue color, which disappears on photocycloaddition, permits exact control over the reaction time. A mixture of thiobenzophenone and a-phellandrene must be irradiated for 70 hr before the blue color disappears (Eq. 2) and... 

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