Use of sultines in the asymmetric synthesis of polypropionate antibiotics

At low temperature and in the presence of an acid catalyst, SO2 adds to 1,3-dienes equilibrating with the corresponding 3,6-dihydro-1,2-oxathiin-2-oxides (sultines). These compounds are unstable above -60 °C and equilibrate with the more stable 2,5-dihydrothiophene 1,1-dioxides (sulfolenes). The hetero-Diels-Alder additions of SO2 are suprafacial and follow the Alder endo rule. The sultines derived from 1-oxy-substituted and 1,3-dioxy-disubstituted 1,3-dienes cannot be observed at -100 °C but are believed to be formed faster than the corresponding sulfolenes. In the presence of acid catalysts, the 6-oxy-substituted sultines equilibrate with zwitterionic species that react with electron-rich alkenes such as enoxysilanes and allylsilanes, generating β,γ-unsaturated silyl sulfinates that can be desilylated and desulfinylated to generate polypropionate fragments containing up to three contiguous stereogenic centers and an (E)-alkene unit. Alternatively, the silyl sulfinates can be reacted with electrophiles to generate polyfunctional sulfones (one-pot, four-component synthesis of sulfones), or oxidized into sulfonyl chlorides and reacted with amines, then realizing a one-pot, four-component synthesis of polyfunctional sulfonamides. Using enantiomerically enriched dienes such as 1-[(R)- or 1-(S)-phenylethyloxy]-2-methyl-(E,E)-penta-1,3-dien-3-yl isobutyrate, derived from inexpensive (R)- or (S)-1-phenylethanol, enantiomerically enriched stereotriads are obtained in one-pot operations. The latter are ready for further chain elongation. This has permitted the development of expeditious total asymmetric syntheses of important natural products of biological interest such as the baconipyrones, rifamycin S, and apoptolidin

Metal- and reagent-free electrochemical synthesis of alkyl arylsulfonates in a multi-component reaction

This work presents the first electrochemical preparation of alkyl arylsulfonates by direct anodic oxidation of electron-rich arenes. The reaction mechanism features a multi-component reaction consisting of electron-rich arenes, an alcohol of choice and excess SO2 in an acetonitrile-HFIP reaction mixture. In-situ formed monoalkyl sulfites are considered as key intermediates with bifunctional purpose. Firstly, this species functions as nucleophile and secondly, excellent conductivity is provided. Several primary and secondary alcohols and electron-rich arenes are implemented in this reaction to form the alkyl arylsulfonates in yields up to 73 % with exquisite selectivity. Boron-doped diamond electrodes (BDD) are employed in divided cells, separated by a simple commercially available glass frit

Characteristics of the Coagulate Obtained During the Process of Model Wastewater Treatment

In the process of wastewater treatment by coagulation a large amount of sediment is being produced, which is the main drawback of this method. Therefore, the development of utilization or recirculation technology of the waste obtained, the research of the obtained by-products should be conducted. Within the scope of this work, the sediment, that is being formed during the coagulation of the model wastewater containing the wood originated pollutants, was studied. Using the aluminium-containing composition coagulant on a base of polyaluminium chloride, coagulates characterized by the low sludge volume index within 30 minutes (89 ml g-1), and the optimal time of sedimentation is 20-30 minutes. The coagulate particles have an average size of 45.8 μm. The derived coagulate is composed primarily of carbon (27.9%), oxygen (49.4%) and aluminum (10.9%). Carbon, oxygen and hydrogen belong to an organic part of coagulate-the wood pollutants, which, in turn, has a high content of hemicellulose. It is concluded that the existing hemicellulose in the obtained coagulate is characterized by O-acetyl-4-O-methyl-D-glucuron-β-D-xylan with β-(1-4)-glucomannose

Use of sultines in the asymmetric synthesis of polypropionate antibiotics

At low temperature and in the presence of an acid catalyst, SO2 adds to 1,3-dienes equilibrating with the corresponding 3,6-dihydro-1,2-oxathiin-2-oxides (sultines). These compounds are unstable above -60 degrees C and equilibrate with the more stable 2,5-dihydrothiophene 1,1-dioxides (sulfolenes). The hetero-Diels-Alder additions of SO2 are suprafacial and follow the Alder endo rule. The sultines derived from 1-oxy-substituted and 1,3-dioxy-disubstituted 1,3-dienes cannot be observed at -100 degrees C but are believed to be formed faster than the corresponding sulfolenes. In the presence of acid catalysts, the 6-oxy-substituted sultines equilibrate with zwitterionic species that react with electron-rich alkenes such as enoxysilanes and allylsilanes, generating beta,gamma-unsaturated silyl sulfinates that can be desilylated and desulfinylated to generate polypropionate fragments containing up to three contiguous stereogenic centers and an (E)-alkene unit. Alternatively, the silyl sulfinates can be reacted with electrophiles to generate polyfunctional sulfones (one-pot, four-component synthesis of sulfones), or oxidized into sulfonyl chlorides and reacted with amines, then realizing a one-pot, four-component synthesis of polyfunctional sulfonamides. Using enantiomerically enriched dienes such as 1-[(R)- or 1-(S)-phenylethyloxyl-2-methyl-(E,E)-penta-1,3-dien-3-yl isobutyrate, derived from inexpensive (R)- or (S)-1-phenylethanol, enantiomerically enriched stereotriads are obtained in one-pot operations. The latter are ready for further chain elongation. This has permitted the development of expeditious total asymmetric syntheses of important natural products of biological interest such as the baconipyrones, rifamycin S, and apoptolidin A

Umpolung of 1-alkoxy-3-acyloxy-1,3-dienes with sulfur dioxide and its application in polypropionate synthesis

Under appropriate conditions sulfur dioxide reacts with 1,3-dienes in the hetero-Diels-Alder fashion. In the case of 1-alkoxy-1,3-dienes the 6-alkoxy-3,6-dihydro-1,2-oxatiin-2-oxides (sultines) so-obtained can be ionized in the presence of Lewis or protic acid, thus realizing Umpolung of these electron-rich systems. The zwitterionic intermediates can be trapped as electrophiles with enoxysilanes (oxyallylation) to generate substituted silyl alkenylsulfinates. Desilylation of the latter under acidic conditions leads to intermediate allylsulfinic acids, which, after retro-ene desulfitation, produce 4-alkoxyhept-6-en-2-one core, a valuable fragment in polyketide natural product synthesis. This new SO2 reaction cascade, hetero-Diels-Alder addition/oxyallylation/retro-ene desulfitation (Vogel's cascade), was expanded to 1,3-dioxy-1,3-dienes. It was demonstrated that 1-alkoxy-3-(trialkylsilyl)oxy-1,3-dienes (Danishefsky's dienes) undergo ene reaction with sulfur dioxide due to migratory properties of trialkylsilyl substituent. The use of 1-alkoxy-3-acyloxy-2-methyl-1,3-pentadienes and enoxysilanes in Vogel's cascades resulted in an efficient synthesis of stereotriads containing keto and enol ester functions, suitable for further chain elongation. Good anti,syn and anti,anti selectivities were achieved using of (Z)- and (E)-enoxysilanes, respectively. The synthetic potential of the method was demonstrated by the short synthesis of 3,5-dihydroxycyclohexanone subunit of baconipyrones A and B as well as that of the hydroxydiketone subunit of baconipyrones C and D ((-)-(4S,6S)-4,6-dimethyl-5-hydroxynonan-3,7-dione). Further applications were shown by expeditious formal asymmetric total synthesis of rifamycin S and initiation of synthesis of C(27)-C(37) fragment of brasilinolides A and C. The method was extended to other π-nucleophiles, such as allylsilanes. A small library of differently substituted homoallylic ethers was synthesized to demonstrate utility of this new approach. Iterative Vogel's cascade employing newly obtained fragments provided long-chain polypropionate fragments such as (-)-(1Z,2S,3S,7S,8R,9R)-1-ethylidene-9-hydroxy-2,8-dimethyl-3,7-bis((1S,1'S)-phenylethoxy)-5-methylene-undec-1-yl benzoate in a very short and efficient way. Further generalization of π-nucleophiles led to the discovery of new ene reactions of SO2 with allylgermanes and allylboronates. A number of new chiral auxiliaries were prepared and tested in order to improve chemo- and diastereoselectivity in diene reactions with sulfur dioxide. The results demonstrated the superiority of inexpensive and readily available 1-arylethanols (and particularly 1-phenylethanol) over other types of chiral auxiliaries

Synthesis of Optically Active 5-Alkoxy-6-methylcyclohex-2-en-1-ones and 4-Alkoxy-5-methylcyclopent-1-enyl Benzoate

The reaction of (-)-(1E,3Z)-2-methyl-1-((1S)-1-phenylethoxy)penta-1,3-dien-3-ol benzoate with allyltrimethylsilane in SO,- and in the presence of a catalytic amount of Tf2NTMS gives a silyl sulfinate intermediate that furnishes (-)-(6Z,1'S,4S,5S)-5-methyl-4-(1'-phenylethoxy)octa-1,6-dien-6-yl benzoate after acidic workup. The latter undergoes ring-closing, metathesis producing (-)-(2S,3S)-2-methyl-3-((1S)-1-phenylethoxy)cyclopent-5-en-1-yl benzoate. It has been converted also into the corresponding trimethylsilyl enol ether. After oxidation, an enone is obtained that undergoes ring-closing metathesis giving (-)-(5S,6S)-6-methyl-5-((1S)-1-phenylethoxy)cyclohex-2-en-1-one