Acylation of N-Boc-N-methylhydrazones followed by TFA treatment affords regioselective access to substituted pyrazoles. Both regioisomers of 1-methyl-3,5-disubstituted-1H-pyrazoles can be selectively obtained. This procedure can also be employed for the regioselective preparation of fully substituted 1H-pyrazoles.

Racemic α-epimerizable and unfunctionalized aldehydes have been converted into enantiomerically enriched mixtures through a sequence of (i) a conversion into the diastereoisomeric 3-substituted 1-phenyl-2,3-dihydro-1H-naphtho[1,2-e][1,3]oxazines by reaction with the (R)- or (S)-1-(α-aminobenzyl)-2-naphthol (Betti's base), (ii) an acid promoted crystallization-induced diastereoisomer transformation (CIDT), and (iii) a clean cleavage of the dihydro-1,3-naphthoxazinic ring of the enriched diastereoisomer, easily collected by filtration, allowing the recovery of the enantiomerically enriched aldehydes and the chiral auxiliary.

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This chapter contains sections titled: Introduction Elliott's Alcohol An Alternative Synthesis of Elliott's Alcohol Comparative Assessment of the Two Alternative Routes to Elliott's Alcohol Driving the “Green” Improvement Conclusions References

Industrial preparation of resmethrin, one of the first members of the pyrethroid family to be introduced, is achieved via Elliott's alcohol. Available procedures make use of stoichiometric amounts of pyridine, thionyl chloride, fuming nitric acid and a lot of chlorinated by-products are generated. We present here an alternative route to Elliott's alcohol, based on Baylis–Hillman reaction in aqueous media. A comparative quantitative assessment of the “greenness” was performed, using the freeware package EATOS which takes into account both the mass economy and the environmental impact of the materials involved.

Five distinct crystal forms of rifaximin (alpha, beta, gamma, delta and epsilon) have been identified and characterised by X- ray powder diffraction, solid state C-13 NMR, and HATR-IR spectroscopy. Changes in the crystal structure may produce differences of two to three orders of magnitude in the rate of intrinsic dissolution, solubility and bioavailability of rifaximin. Alteration of the pharmacokinetic parameters is of particular interest; the C-max values of the crystal forms range from 1.1 to 1085.31 ng ml(-1) and the AUC(0-24) h values range from 10 to 4795 ng h ml(-1). These findings are relevant to the therapeutic use of rifaximin.

Nitroalkanes can be profitably employed as carbanionic precursors for the assembly of dihydroxy ketone frameworks, suitable for the preparation of spiroketals. The carbon-carbon bond formation is carried out exploiting nitroaldol and Michael reactions, while the nitro to carbonyl conversion (Nef reaction) ensures the correct introduction of the keto group. Several spiroketal systems endowed with considerable biological activity can be prepared using this synthetic strategy.

A greatly improved procedure for the preparation of long-chain α-ketopyridazines, a class of potent inhibitors of fatty acid amide hydrolase (FAAH), is described. This optimization study shows a great dependence of the yields of desired products on the pyrididazinyl lithium/Weinreb amide ratio and offers a general approach to this kind of compound.

We have carried out an experimental and computational study on the ground- and excited-state photochemical and photophysical properties of (1-cyclohexenyl)phenyldiazene (CPD), a species formally derived from azobenzene in which one of the phenyl rings is replaced by a 1-cyclohexene substituent. The results show that CPD does substantially behave like azobenzene, but with a higher (approximately 70%) Phi(Z-->E) (npi*) photoisomerization quantum yield, calling for CPD as an effective alternative of azobenzene itself with new functionalization possibilities. By use of state-of-the-art ab initio CASPT2//CASSCF minimum energy path computations, we have identified the most efficient decay and isomerization routes of the absorbing singlet (pipi*), S1 (npi*), T1, and S0 states of CPD. The resulting mechanistic scheme agrees with experimental findings and provides a rationale of the observed photoisomerization quantum yields. Furthermore, this study provides a deep insight on the photophysical and photochemical properties of compounds based on the -N=N- double bond which supplies a general model for the photoreactivity of azobenzene-type compounds in general. This is expected to be a useful guideline for the design of novel photoreactive azo compounds.

The enantiomers of threo-dimethylamino-1-[4-(methylthio)phenyl]propane-1,3-diol (MTDP) were found to be effective resolving agents for trans-chrysanthemic acid (trans-ChA) on an industrial scale. (1S,2S)-(+)-MTDP and (1R,2R)-(−)-MTDP were revealed to be “blind” towards the enantiomers of cis-ChA. They work well on racemic and/or scalemic trans/cis mixtures of industrial production and are used in a stoichiometric amount with respect to the enantiomer of trans-ChA to be collected. Isopropyl ether is the solvent of choice, and it does not need the presence of co-solvents such as methanol to promote nucleation and crystal growth of the n salts as previously reported for threo-dimethylamino-1-[4-(nitro)phenyl]propane-1,3-diol (DMAD) enantiomers. X-ray crystal structures of the n salts of trans-ChA and MTDP revealed the peculiar features of two pseudopolymorphs. MTDP enantiomers are low cost, non-toxic, safe, and easily available from important precursors of thiamphenicol through a single straightforward reaction. After the resolution, they can be recovered almost quantitatively and reused without any loss of their chiral integrity. Similarities and differences of these resolving agents for trans-ChA with respect the behaviour of the enantiomers of DMAD and of the enantiomers of the parent compound, 1-phenyl-2-dimethylamino-1,3-propane-diol (DMPP), are shown in a comparative analysis of their performances.