No abstract

The chlorination of thiane 1-oxides containing large substituents gave -chloro sulfoxides with the chlorine atom in the axial and the oxygen atom in the equatorial position, independent of the configuration at the sulfur of the starting material. Thiane 1-oxides containing small substituents do not undergo a sulfur but, rather, a ring inversion to place the oxygen in the equatorial position before being halogenated axially at the a positions. Stereochemically different products are obtained from different stereoisomers containing small substituents. The halogenation mechanism is assumed to proceed by way of a tetrahedral chlorosulfoxonium ion containing the oxygen in an equatorial position. Subsequent concerted trans-diaxial elimination of hydrogen chloride to give an "inverted ylide" followed by axial chloride ion attack leads to the observed products. Sulfoxideswere recently found to be very easily chlorinated at the a position by a number of halogenating agents such as nitrosyl chloride,1 phenyliodonium dichloride,2 rm-butyl hypochlorite,3 /Holuenesulfonyl chloride,4 chlorine,5 sulfuryl chloride,6-7 and 1-chlorobenzotriazole.8 This great activity was aroused by the interest in the mechanism of exchange of hydrogens a to sulfinyl groups proceeding by a carbanion mechanism and, in general, the mechanism of substitution ato a sulfoxide group, which may be considered an analog of the carbonyl group. The stereochemical course of the hydrogen exchange is influenced by the kinetic acidity of the different hydrogens and the rate of interconversion and the stability of the isomeric anion.9-22 Chlorination was assumed to proceed5'23 by a first step proton abstraction followed by the reaction of the sulfinylcarbanion with chlorine (reaction 1). This mechanism does not seem probable since halogenation is very fast even at low temperatures and in the presence

The ionization in aqueous sulphuric acid of thiolactams consisting of five-, six-, and sevenmembered rings has been studied. With increasing concentration of acid the ionization ratio increases more rapidly than ho. A possible explanation involving the hydration of the thiolactam is given. Changes in the basicity of thiolactams with ring size parallel changes previously found for lactams.By analogy with the resonance structures of simple amides (I), the structure of lactams (I; X = 0 ) would be expected to be made up by a 60y0 contribution from structure Ia (X = 0 ) and 40% contribution from structure Ib (X = 0), although the relative weights of the contributions could be altered somewhat by ring strain (2). Thiolactams (I; X = S) have higher dipole moments (3), and so should be represented to a preponderant extent by the dipolar form I b (X = S). The high polarity of the thiolactams (I; X = S, n = 3 , 4 , and 5) may in part account for the fact that they are solids a t room temperature while the corresponding lactams (I; X = 0, n = 3, 4, and 5 ) are liquid, and that (as postulated later in this paper) they appear to be more extensively hydrated in a-queous solution than are the lactams.It is probable that lactams and thiolactams in strong acid are protonated on the oxygen or sulphur atom to give the conjugate acids (11; X = 0 or S) (4). Consequently i t became of interest to compare the basicities of the two classes of compounds. I t seemedpossible that in spite of the greater intrinsic basicity of oxygen as compared with sulphur (cf. OH-and SH-), the greater negative charge on the sulphur of thiolactams would cause them to be more basic than lactams. We have accordingly determined the protonation constants of the thiolactams (I; X = S, n = 3, 4, and 5) for comparison with the protonation constants reported for the lactams (I; X = 0 , n = 3, 4, and 5) (2).

M et h y I ati o n of 5 pc h o I es t -7 -en -3o n e y i e I ds 2 pmet h y I -5 pc h o I e st -7 -en -3 -one and 2,2 -d i met h y I -5 pc h o I es t-7-en-3-one. The structure of the former was proven by its conversion into the known 2p-methyl-5p-cholestan-%one; the structure of the latter was established from the mass spectrum of its ethylene acetal. Use is made of Bucourt's rules of dihedral angle changes in describing the conformational transmission effects which may account for methylation at C-2 rather than a t C-4.

Thiane, die keine 4‐OH‐oder 4‐O‐Gruppe besitzen wie z.B. (I), werden durch Brom in Gegenwart von Wasser vorwiegend zum äquatorialen Thianoxid wie z.B. (II) oxidiert.