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Fifteen imidazo[2,1-b]thiazoles containing a range of substituents at position 6 have been used in studies of electrophilic substitution at position 5. Acid-catalysed deuteriation, was examined quantitively and, by making certain assumptions, values for the rate constants (k1) of the deuteriation process were obtained. A 3-methyl group increases k1 by a factor of ca. 3; for different 6-substituents the k1-values are in the order Me > But∼ C6H4OMe-p > Ph. Bromination occurred preferentially at position 5 even with substrates containing 6-substituents (e.g., 2-thienyl) which themselves have a reactive nucleus. Although 6-alkyl-5-nitrosoimidazothiazoles are unstable and cannot be prepared by the standard method (sodium nitrite and acetic acid), the 6-t-butyl compounds were obtained by a procedure in which the work-up involves very mild treatment. The 5-formyl derivatives show extensive mesomerism, and in solution they adopt the conformation having the carbonyl oxygen syn to N(4). In one compound, the 4,6-dimethyl-5-carbaldehyde, the anti rotamer is present as the minor component. Imidazo[2,1-b]thiazoles are easily converted into 5-trifluoroacetyl compounds and 5-thiocyanates.

Two methods have been used for epimerising the 3-hydroxy-group of 19-norergosta-5,7,9-trien-3β-ol. Although the 3β- and 3α-alcohols show a close resemblance in many of their properties it is possible to distinguish between them by examining the 19F n.m.r. spectra of their α-methoxy-α-trifluoromethylphenylacetates and the 1H n.m.r. spectra of their complexes with shift reagents. Purification of the alcohols is most reliably achieved by crystallising their 3,5-dinitrobenzoates. Measurement of optical rotation is the best method for the quantitative analysis of mixtures of the epimers.

Known methods were developed to give convenient general procedures for preparing N-acyl-N′-mono and -N′,N′-disubstituted thioureas from acid chlorides, and related N-imidoyl thioureas from imidoyl chlorides. In the products from three acid chlorides and ammonium thiocyanate the acyl isothiocyanates did not appear to be accompanied by the isomeric thiocyanates.Treatment of N-(anilino)benzylidene-N′,N′-disubstituted thioureas with chloroacetone in the presence of triethylamine leads to 5-acetyl-4-phenyl -2-(N,N-disubstituted amino)thiazoles. In contrast, the corresponding N-benzoyl thioureas form only small amounts of these compounds; the main products are the 5-benzoyl-4-methyl isomers, and this unexpected outcome requires a revision of the literature. It is thought that formation of the 5-benzoyl-4-methylthiazoles involves N–C(4) fission of a cyclic intermediate to give an open-chain intermediate in which nucleophilic attack can occur at either the acetyl or the benzoyl group. One of the latter intermediates was generated directly from 2-acetyl-2-bromoacetophenone and N-methyl-N-phenylthiourea, and found to give the 5-benzoyl-4-methyl - and 5-acetyl-4-phenyl-thiazoles as the major and minor products, respectively.

Dioxo-5α-androstanes having one keto-group in a terminal ring (at position 3 or 2, or at position 17) and the second at a middle ring position (7 or 11) are hydroxylated in the other terminal ring (at 17 or 16, or at 3 or 2) by the fungi Wojnowicia graminis and Ophiobolus herpotrichus. Efficient transformations include the 2α-hydroxylation of 5α-androstane-7,17-dione (with W. graminis), the 16-substitution of the 3,11-dione (with O. herpotrichus), and the 17β-hydroxylation of 3,7-dioxygenated substrates (with both fungi).

Mono- and di-ketones and keto-alcohols derived from 5α-androstane have been incubated with the fungus Daedalea rufescens, a Basidiomycete species not previously reported as a steroid hydroxylator. All but one of the dioxygenated substrates, and the monoketones with the keto-group in a central ring, are hydroxylated fairly rapidly. The cleanest hydroxylations occur with 7-oxygenated androstanes and lead to the 3β,16β-dihydroxy-derivatives.Incubation of 3,3-ethylenedioxy-5α-androstan-7-one (in which hydroxylation is accompanied by reduction of the 7-keto-group) followed by hydrolysis of the product gives 7α,16β-dihydroxy-5α-androstan-3-one in 57% yield.

A series of monofluoro- and gem-difluoro-5α-androstanones and the parent ketones were incubated, under standard conditions, with the fungi named in the title. The results may be rationalised by comparing the positions of the fluorine atoms in the substrates with those of the favoured hydroxylation sites in the parent ketones. With few exceptions hydroxylation does not occur at, or adjacent to, the carbon to which a fluorine substituent is attached even though one of these centres is a favoured site (in the parent ketone). In such cases hydroxylation is usually diverted to an alternative position. Where the favoured site is more distant from the fluorine substituent(s) the behaviour of a fluoro-ketone resembles that of its parent. Hydroxylation of several fluoro-ketones by Aspergillus ochraceus gives the 11 α-hydroxy-derivatives cleanly and in yields which are satisfactory for preparative work.

The sequence of microbiological reactions involved in the 19-hydroxylation of 5α-androstan-17-one has been established. When a solution of 5α-androstan-17-one in dimethyl sulphoxide is incubated with Calonectria decora, the initial 1β,6α-dihydroxylation is followed by oxidation of the 1β-hydroxy-group and then by hydroxylation at C-19 to give 6α,19-dihydroxy-5α-androstane-1,17-dione in 36% yield. This compound is readily transformed (by chemical methods) into 5α,10β-estrane-1,6,17-trione.C-19 hydroxylation occurs also with certain substituted 17-oxo-5α-androstanes and 17-oxo-3α,5-cyclo-5α-androstanes.

Hydroxylation of 3β-hydroxy-5α-pregnan-20-one with Aspergillus ochraceus, in shake-flasks or using 10g batch fermentation, gives 1β,3β,11α-trihydroxy-5α-pregnan-20-one as the main product (ca. 50% yield); this trihydroxy-ketone is readily converted into 5α-pregn-1-ene-3,11,20-trione. With some other 20-oxo-5α-pregnanes containing a second oxygen group, the initial 11α-hydroxylation is followed by a variety of processes which lead to mixtures of products.

Diketones and keto-alcohols derived from 5α-androstane are readily converted into monohydroxy-derivatives by Rhizopus nigricans. Varying the positions and oxidation levels of the oxygen functions leads to hydroxylation at different positions. Substrates with one oxygen substituent in each of the terminal rings are attacked at position 11 or 7; those with one group in rings B or C are hydroxylated at position 16 if the second group is in ring A, and at position 3 if the second group is in ring D.The results are rationalised by assuming the presence of three dual-purpose sites on the enzyme surface capable of binding to the steroidal oxygen groups and of hydroxylating those positions of the steroid nucleus which come into their vicinity.

4,4-Dimethyl-5α-androstan-2-one and lupan-2-one, preapared from the 3-ketones by general methods for transposing oxo-groups, undergo substitutions at position 3. Acetoxylation and bromination proceed easily and introduce 3α-substituents; formylation to the 3-hydroxymethylene-2-ketones is difficult and gives poor yields even under forcing conditions.

The hydroxylations of seven diketones and keto-alcohols derived from 5α-androstane with Rhizopus arrhizus and Rhizopus circinnans are similar to, but not identical with, those observed previously using Rhizopus nigricans. R. circinnans is useful for introducing a 4α-hydroxy-group into 5α-androstane-11,17-dione.N.m.r. shift values are given for the influence on steroidal 18- and 19-H signals of various single substituents, and of systems containing two or more substituents whose effects are not additive.

Diaporthe celastrina, a fungus not previously reported as being active with steroids, hydroxylates a range of dioxygenated 5α-androstanes generally by attack on the α-face. The sites of hydroxylation and the efficiencies of the processes depend on the positions and oxidation levels of the androstanes' substituents. 5α-Androstane-3,7-dione is converted into 3β,16α-dihydroxy-5α-androstan-7-one (45% yield); 3β-hydroxy-5α-androstan-17-one is hydroxylated in the 9α-position (55%), and 5α-androstane-7,17-dione gives the 3α-hydroxy-derivative (52%).

Eight 3,20-, 7,20-, and 11,20-dioxygenated 5α-pregnanes have been incubated with the fungi Calonectria decora and Daedalea rufescens, and with three Rhizopus species. In most cases complex mixtures are formed, and the hydroxylations are less satisfactory than those of dioxygenated androstane analogues. Although Rhizopus nigricans leads mainly to the 11α-hydroxylation of 5α-pregnane-3,20-dione, hydroxylation of 3β-hydroxy-5α-pregnan-20-one occurs predominantly at the 7β-position (not at the 11α-position as reported in the literature). The cleanest incubation studied here is that of 5α-pregnane-7,20-dione with Calonectria decora, which gives the 1α,12β-dihydroxy-7,20-dione (30%) and the 12β-hydroxy-1,7,20-trione (19%).Convenient preparations of the 7,20- and 11,20-dioxygenated substrates have been developed.

The hydroxylations set out in the title have been studied and the results compared with those (obtained in earlier work) of hydroxylating the parent 3-, 7-, and 17-ketones. The microbiological effect of a halogeno-substitutent depends on its nature, position, and configuration in the steroid nucleus. The 3α-fluoro-, 3α-chloro-, and 3α-bromo-5α-androstan-17-ones undergo 1β,6α-dihydroxylation with C.decora; while the 3β-chloro- and 3β-bromo-analogues are more reactive (and are also hydroxylated initially in this way), the 3β-fluoro-17-ketone is recovered essentially unchanged. Loss of halogen generally occurs during incubations of 3-halogeno-17-ketones with R.nigricans, the products being 3-oxo- and 3β-hydroxy-compounds. A.ochraceus converts the fluoro-ketones (but not the chloro-ketones) into their 11α-hydroxy- or 7β,11α-dihydroxy-derivatives; the former process has been utilised in the preparation of 3α- and 3β-fluoro-5α-androstane-11,17-dione.

Acetals and enol ethers derived from oxoandrostanes are less reactive than the parent ketones towards the title fungi. None of the derivatives is hydroxylated by Rhizopus nigricans, and only one by Aspergillus ochraceus. With Calonectria decora the acetals generally give patterns of hydroxylation similar to, but less specific than, those of the corresponding ketones. 16,16-Ethylenedioxy-5α-androstane is exceptional in that its hydroxylation with Calonectria decora to a 6α,12β-dihydroxy-product is more efficient than the 6α,11α-dihydroxylation of 5α-androstan-16-one.

Although steroidal monoketones with the carbonyl group in ring B or C are relatively unreactive towards Rhizopus nigricans, 2-, 3-, 16-, and 17-ketones give modest yields of dihydroxy-derivatives. The position of the carbonyl group influences the direction of the hydroxylation process: comparison of the 11,16-dihydroxylation of 3-ketones with the 3,7-dihydroxylation of 17-ketones suggests that a reversal effect is operating.16-Hydroxylation, not previously recorded with this fungus, occurs commonly with the present androstane and estrane derivatives, i.e. steroids lacking side-chains at position 17. Estr-4-en-3-one gives three 16-oxygenated products (total yield 68%), the main one being the 10β,16β-dihydroxy-Δ4-3-ketone.

The mechanisms of two reactions which give isomeric thiazol-5-yl ketones have been elucidated by work with substrates containing pairs of acyl groups and their deuterium-substituted analogues.

A convenient procedure for preparing N-mono- and N,N-di-substituted cyanamides from cyanogen bromide has been developed. N,N-Disubstituted thioureas, obtained from the cyanamides, were condensed with α-bromo-α-cyano-ketones to give 5-cyano-2-(N,N-disubstituted amino)thiazoles and with α-bromo-ketones to give 2-(N,N-disubstituted amino)thiazoles. Substitution in the latter products afforded 5-trifluoroacetyl- and 5-nitro-2-(N,N-disubstitutedamino)thiazoles; nitration is greatly facilitated by the presence of a 4-aryl group.The average values of the barriers to rotation of the 2-NR2 groups (ΔG‡298) in the 5-substituted thiazoles were established by variable temperature 1H n.m.r. spectrometry to be 57.4 kJ mol-1(5-NO2), 56.2 (5-COCF3), and 51.5 (5-CN). I.r. examinations showed that the 5-trifluoroacetyl compounds adopt one rotational form preferentially; this is probably the carbonyl O,S-syn-conformation.

The conformational preferences of 2-(N,N-disubstituted amino)thiazoles having a 4-substituent (R1) and a 5-acyl group (R2CO) have been established by i.r. spectrometry and a crystallographic examination. In solution the compounds with R2= aryl and R1= Me or aryl exist predominantly or entirely in the carbonyl O,S-anti arrangement; for those with R1= aryl and R2= Me the syn rotamer is the main form but a small amount (ca. 15%) of the anti rotamer is present.Nitrosation of 4-aryl-2-dimethylaminothiazoles gives 5-nitroso derivatives, and these are probably the first authentic nitrosothiazoles. The barrier to rotation of the dimethylamino group is unexpectedly high (ΔG298‡= 69 kJ mol–1), exceeding even that of the 5-trifluoroacetyl analogues.

The NH and CO bands of solutions of pyrrole-2-carboxylates, pyrrole-2-carbaldehydes, and their N–Me analogues have been studied. Knowledge gained from the spectra of the aldehydes, which are known to adopt the N,O-syn-conformation, was applied in deducing the conformational preferences of the esters from their i.r. absorptions. The N-Me esters exist predominantly or exclusively in the N, carbonyl O-syn-arrangement. With the N–H esters both syn- and anti-rotamers are present, the former predominating, and in the case of t-butyl pyrrole-2-carboxylate the syn-form was shown to be thermochemically more stable than the anti-form by ca. 4.8 kJ mol–1. The intermolecular associations of pyrrole-2-carbaldehyde and of t-butyl pyrrole-2-carboxylate give species containing more than two molecules of the substrates and involve similar enthalpy changes (ca. 22 kJ mol–1).

A study has been made of the condensations between N-acyl-N′,N′-disubstituted thioureas and α-halogeno ketones [reaction (I)], and between N,N-disubstituted thioureas and 2-bromo-1,3-diketones [reaction (II)]. The mechanistic details were elucidated by using substrates with pairs of (almost) equally reactive but spectrometrically distinguishable acyl groups, e.g., CH3CO and CD3CO. In the presence of added base (triethylamine) both reactions proceed through a common open-chain 1,3-diketone; from this, isomeric products are formed by nucleophilic attack at the alternative carbonyl groups to give cyclic intermediates which then undergo rate-limiting dehydration. If base is not added the media become acidic. Reaction (II) follows its previous course but the relative rates of the stages are reversed. In reaction (I) the initial cyclic intermediate is dehydrated so rapidly that the open-chain 1,3-diketone is not formed, and only one isomer is produced.Both reactions are useful preparatively. For example, by adding or omitting triethylamine a typical reaction (I) was induced to give 1-(5-p-methoxybenzoyl-4-p-nitrophenylthiazol-2-yl)hexahydroazepine (yield 79%) or the isomeric 4-p-methoxyphenyl-5-p-nitrophenyl compound (78%).

5-Acetyl-2-(N,N-disubstituted amino)thiazoles, unsubstituted or with Me, But, or Ph groups at position 4, have been prepared by unambiguous methods and examined spectrometrically; crystallographic studies have been carried out on four of the compounds and a related 4-aryl-5-trifluoroacetylthiazole. In solution the 4-H, 4-But, and 4-Ar compounds exist predominantly in one conformation but with the 4-Me compounds, two forms (carbonyl O,S-syn or anti, related by rotation of the 5-acetyl group) of approximately equal stability are present. The X-ray work establishes that for 5-acetylthiazoles, as solids, the 4-H and 4-Ph derivatives have the carbonyl O, S-syn stereochemistry whereas the 4-Me and 4-But derivatives have the anti arrangement; in contrast with the 5-acetyl-4-phenyl compound the 4-aryl-5-trifluoroacetylthiazole adopts the anti arrangement. These findings validate a correlatioh, for solutions, between the stereochemistry of the rotational isomers and the positions of their i.r. CO bands.The results confirm the operation of a strong mesomeric interaction between the 2-NR2 and 5-CH3(CF3)CO groups.

Solutions of α-mercapto-ketone anions, generated from O-ethyl S-2-oxoethyl dithiocarbonates and piperidine, react with cyanamides to give 2-aminothiazoles with substituents on the heterocycle or the exo-nitrogen atom.

Efficient methods for the preparation of the compounds listed in the title have been developed. Examination of their 1H n.m.r. spectra showed that in these substituted dihydronaphthalenes the ring containing the olefinic bond is conformationally mobile. Study of the deuteriated derivatives was useful in interpreting the gross spectrometric features of the parent compounds but did not simplify the detailed analysis.

Methods for preparing N,N-disubstituted 2-aminothiazoles have been investigated. 4-Substituted N,N-dimethyl-, N-benzyl-N-methyl-, and N-methyl-N-phenyl-amines were prepared and converted by Vilsmeier formylation into 2-amino-5-carbaldehydes which were examined by i.r. and 1H n.m.r. spectrometry. The aldehyde group adopts the carbonyl O,S-syn-conformation. With the N,N-dimethyl and N-benzyl-N-methyl compounds the barrier to rotation of the amine group (ΔG‡) is 50–55 kJ mol–1 and is insensitive to the nature of the 4-substituent. The amine group of the N-methyl-N-phenyl compounds has a marked preference for one orientation. This was shown by a crystallographic study of 4-t-butyl-2-(N-methyl-N-phenylamino)thiazole-5-carbaldehyde to have the phenyl group directed towards the sulphur atom of the thiazole ring.The results of the physical methods overlap in establishing the importance of a mesomeric interaction between the functional groups of 2-aminothiazole-5-carbaldehydes.

The O–H stretching absorptions of aryldi-t-butylmethanols are composed of three symmetrical bands. These are assigned to antiperiplanar H–O–C–Ar arrangement, and two synclinal forms which are distinguished by the presence or absence of O–H ⋯π-electron interaction. N.m.r. evidence suggests that interconversion between the synclinal forms, involving only a partial rotation about the Ar–C axis, is rapid at 34 °C; complete rotation is more severely impeded.The measurement of enthalpy differences confirms the occurrence of intramolecular bonding in benzyl alcohol and dimethylphenylmethanol.