Stereospecific alkylation of 3,5,5-trisubstituted-4-hydroxy-1-p-tosyl-2-pyrazolines by trimethylaluminum. An efficient synthesis of 3,3,5,5-tetrasubstituted-1-pyrazolin-4-ones

Formation of 5-alkylidenepyrazol-4(1H)-ones and 3-amino-6-aryl-5-cyano-pyridazine-4-carboxylates from arenealdehyde thiosemicarbazones and unsaturated 1,2-diesters

The reaction of arenealdehyde 4-phenylthiosemicarbazones 1a–f with dimethyl ethynedicarboxylate (6) gave methyl [3-aryl-4-oxo-1-(phenylthiocarbamoyl)-4,5-dihydro-1H-pyrazol-5-ylidene]ethanoates 10a–f in 73-79% yield, while, by reaction with diethyl (E)-2,3-dicyanobutenedioate (7), compounds 1a–f are transformed into ethyl [3-aryl-4-oxo-1-(phenylthiocarbamoyl)-4,5-dihydro-1H-pyrazol-5-ylidene]cyanoacetates 15a–f (54-61%) and ethyl 3-amino-6-aryl-5-cyanopyridazine-4-carboxylates 24a–f (22-26%). Rationales for these transformations are presented.

First Direct Detection of 2,3-Dimethyl-2,3-diphenylcyclopropanone

3,5-dihydro-3,5-dialkyl-3,5-diaryl-4H-pyrazol-4-ones stimulate interest as potential precursors for 2,3-diarylcyclopropanones. Photoreactions of trans-3,5-dihydro-3,5-dimethyl-3,5-diphenyl-4H-pyrazol-4-one were studied by continuous-wave (CW) and pulsed laser UV photolysis revealing an intermediate that undergoes rearrangement to form cis- and trans-1,3-dimethyl-1-phenyl-2-indanones with the yield of ca. 60%. Steady-state photolysis (254 and 350 nm excitation) in different solvents produced an intermediate cyclohexadiene as evidenced by UV/vis, IR, and 1H NMR spectra. In contrast, the nanosecond laser pulsed photolysis at 355 nm produced 2,3-dimethyl-2,3-diphenylcyclopropanone along with two products of retro-1,3-dipolar addition phenylmethylketene and 1-phenyldiazoethane. These can be observed by time-resolved IR (TRIR) spectroscopy as characteristic absorption bands at 1814, 2101, and 2038 cm-1, respectively. Similar retro-1,3-dipolar addition showed 1-phenyldiazoethane formed following flash photolysis of 1-pyrazoline (trans-4,5-dihydro-3,5-dimethyl-3,5-diphenyl-3H-pyrazol-4-ol). The formation of the corresponding cyclopropanone as well the products of retro-1,3-dipolar addition during photoreaction of starting pyrazol-4-one is directly confirmed by the nanosecond TRIR spectroscopy for the first time. On the basis of the CW and pulsed laser UV photolysis, a dynamic equilibrium between cyclopropanone and intermediate 2,4-diphenyl-3-pentanone-2,4-diyl (dimethyldiphenyloxyallyl) was proposed.

Ochtodene derivatives from the red alga Carpopeltis crispata

Red algae are well known as a source of halogenated monoterpenes such as derivatives of ochtodene. From Carpopeltis crispata, we have isolated four new ochtodene derivatives: dibromodichloro-, dibromochloro-, and bromodichlorocyclomonoterpenes. The structures of these monoterpenes were confirmed by NMR and mass spectroscopy and compared with spectral data in the literature.

Apakaochtodenes A and B: two tetrahalogenated monoterpenes from the red marine alga Portieria hornemannii

The structure of apakaochtodene A, the minor isomer of two tetrahalogenated ochtodene monoterpenes, isolated from the red marine alga Portieria hornemannii (Lyngbye) Silva has been identified as 6(S)-bromo-1,4(S),8(R)-trichloro-2(Z)-ochtodene (1) by NMR spectral and X-ray crystallographic analysis. Its geometrical isomer, apakaochtodene B (2), which could not be separated from 1 and thus characterized as a 95:5 mixture of 2:1 had (1)H and (13)C NMR spectral characteristics similar to previously known ochtodene (3) and the related tetrahalogenated monoterpene 4.