Condensation of unsaturated cyclic sulfones with aldehydes

The reactivity of the 2(5) positions of dihydrothiophene dioxide has been studied. Their condensation with aldehydes leads to the formation of 2(5)-substituted derivatives containing a conjugated system of double bonds.     

Blacklight-Induced Hydroxylation of Arylboronic Acids Leading to Hydroxyarenes Using Molecular Oxygen and Tetrabutylammonium Borohydride

A new simple protocol for the conversion of arylboronic acids to hydroxyarenes was achieved using molecular oxygen in the presence of tetrabutylammonium borohydride under blacklight irradiation (360 nm). A radical chain mechanism in which a superoxide ion (O₂^−.) plays a key role is proposed.     

Condensation of unsaturated cyclic sulfones with aldehydes

The reactivity of the 2(5) positions of dihydrothiophene dioxide has been studied. Their condensation with aldehydes leads to the formation of 2(5)-substituted derivatives containing a conjugated system of double bonds.     

Synthesis and antibacterial activity of hydroxylated 2-arylbenzothiazole derivatives

Abstract

N-acyliminium reagents formed in situ from benzothiazole and alkyl chloroformates react with hydroxyarenes in a Friedel-Crafts manner, providing access to 2-(hydroxyaryl)-benzothiazolines with antibacterial properties.     

The synthesis of substituted 2,3-dihydrothieno[2,3-b]-thiophenes via intramolecular michael addition

The first regiospecific synthesis of the 2,3-dihydrothieno[2,3-b]thiophene ring system was achieved using an intramolecular Michael addition in the key cyclization step. This strategy represents a novel and potentially general method for dihydrothiophene and dihydrothiophene S,S-dioxide annellation.     

Catalytic properties of Sn-Ce-Rh-O in dehydrogenation and oxidative dehydrogenation reactions

A new, single-phase Sn_0.925Ce_0.07Rh_0.005O₂ gas sensitive material has up to now been used as a catalyst for the bimolecular condensation of aldehydes and C-alkylation of hydroxyarenes with alcohols. It was subjected to the isopropanol test, the oxidative dehydrogenation of cyclohexane test, and the cyclohexene + H₂ test. A general physico-chemical analysis was done, and it included XRD, SEM, mercury porosimetry, TPD NH₃, and IR (pyridine) spectroscopy. The tests results are compliant with the basic character of the catalyst; however, it reveals significant total acidity (0.274 mmol NH₃/g) and the presence of Lewis strong acid centers (0.126 mmol Py/g). The presence of these centers in the dehydrogenating catalysts cause the ability to catalyze both the bimolecular condensation of aldehydes and C-alkylation of hydroxyarenes with alcohols. Published in Russian in Kinetika i Kataliz, 2007, Vol. 48, No. 1, pp. 74–80. The article was submitted by the authors in English.     

A new type of excited-state intramolecular proton transfer: proton transfer from phenol OH to a carbon atom of an aromatic ring observed for 2-phenylphenol

The photochemical deuterium incorporation at the 2'- and 4'-positions of 2-phenylphenol (4) and equivalent positions of related compounds has been studied in D(2)O (CH(3)OD)-CH(3)CN solutions with varying D(2)O (CH(3)OD) content. Predominant exchange was observed at the 2'-position with an efficiency that is independent of D(2)O (MeOD) content. Exchange at the 2'-position (but not at the 4'-position) was also observed when crystalline samples of 4-OD were irradiated. Data are presented consistent with a mechanism of exchange that involves excited-state intramolecular proton transfer (ESIPT) from the phenol to the 2'-carbon position of the benzene ring not containing the phenol, to generate the corresponding keto tautomer (an o-quinone methide). This is the first explicit example of a new class of ESIPT in which an acidic phenolic proton is transferred to an sp(2)-hybridized carbon of an aromatic ring. The complete lack of exchange observed for related substrates 6-9 and for planar 4-hydroxyfluorene (10) is consistent with a mechanism of ESIPT that requires an initial hydrogen bonding interaction between the phenol proton and the benzene pi-system. Similar exchange was observed for 2,2'-biphenol (5), suggesting that this new type of ESIPT is a general reaction for unconstrained 2'-aryl-substituted phenols and other related hydroxyarenes.     

Trifluoromethanesulfonic acid mediated Friedel-Crafts reaction of (E)-3-aryl-2-(diethoxyphosphoryl)acrylic acids with electron-rich hydroxyarenes. A convenient approach to α-methylene-δ-valerolactones

The synthesis of trans-3-diethoxyphosphoryl-4-aryl-3,4-dihydrocoumarins from electron-rich hydroxyarenes and (E)-3-aryl-2-(diethoxyphosphoryl)acrylic acids has been achieved by using CF₃SO₃H as a catalyst. The products could be easily transformed to the corresponding α-methylene-δ-valerolactones by means of the Horner-Wadsworth-Emmons reaction.     

Nucleophilic substitution reaction at an sp carbon of vinyl halides with an intramolecular thiol moiety: synthesis of thio-heterocycles

This article presents a full account of intramolecular vinylic substitution reactions of bromoalkenes having an acetylthio moiety, which give sulfur-containing heterocycles such as dihydrothiophene, tetrahydrothiopyran, and 2-alkylidenethietane derivatives. The reaction pathways of the substitution reactions were investigated by theoretical and experimental studies.     

Cyclic sulfoxides. I. dihydrothiophene 1-oxides

Although there have been extensive investigations on cyclic sulfones, especially the unsaturated, 5-membered ring compounds (3), cyclic sulfoxides have received considerably less attention. In this report, we wish to present a synthesis of the previously unknown dihydrothiophene 1-oxide isomers and, also, some preliminary results regarding their chemical reactivity (4).     

Cycloaddition of CO2 and CS2 to a cyclic phosphazene

Carbon dioxide and carbon disulfide give crystalline cycloadducts with the phosphazene bond of a 1,2λ⁵‐azaphosphole. The CO₂‐adduct fully dissociates in solution, the CS₂‐adduct on short heating only to a small part. On longer heating, the latter rearranges in two successive 1,3‐shifts to give a thiophosphinylimino dihydrothiophene, the structure of which is revealed by X‐ray analysis. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10:167–170, 1999     

Photochemical ring closure of α,α-bisulfenylated carbonyl compounds: Stereoselective formation of cix-dihydrobenzothiophenes

Photochemistry of α,α-bisulfenylated ketone has been investigated. Irradiation of 2-phenylthiodihydrothiophen-3-one (1) in benzene gave the radical recombination products 9 (63%) and 10 (49%). In a polar solvent, the ionic chemistry became predominant. Brief irradiation of 1 in acetonitrile and methanol gave the cis-fused dihydrothiophene 11 as the major product in 43% and 20% yields, respectively. The stereoselective photocyclization was generally observed for other ketones (2–8) in acetonitrile solution (Table 1). The photo-products were easily dehydrated by treating with boron trifluoride etherate to give the corresponding benzothiophenes in high yields. Simple α-phenylthioketones are photoinert under the same conditions. The mechanism of this novel photocyclization of bisulfenylated ketones is also discussed.     

Conformation of substituted five-membered rings

Proton magnetic resonance chemical shifts and coupling constants for some 5-substituted dihydrofurans, dihydrofuran and dihydrothiophene fused rings are reported, the substituents being methyl, ethyl and phenyl. The observed coupling constants are consistent with buckled rings, in which it appears that a conformation with pseudo-equatorial substituents is predominant.     

Polymerization behavior of 2,5‐bis(dicyanomethylene)‐ 2,5‐dihydrofuran

2,5‐Bis(dicyanomethylene)‐2,5‐dihydrofuran (TCNF) is not homopolymerizable with any initiators, but copolymerizable with styrene (St) in an alternating fashion. Reactivity of TCNF was compared with that of 2,5‐bis(dicyanomethylene)‐2,5‐dihydrothiophene (TCNT) on the basis of the terpolymerization of the TCNT‐TCNF‐St system and the rates of addition reactions of AIBN with TCNT and with TCNF. TCNF was found to be lower in reactivity than TCNT. The relative reactivity was explained with the energy difference between quinonoid structure and benzenoid one. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1285–1292, 1999     

Stereoselective synthesis of conformationally constrained 2'-deoxy-4'-thia beta-anomeric spirocyclic nucleosides featuring either hydroxyl configuration at C5'

An enantioselective approach to 2'-deoxy-4'-thia spirocyclic nucleosides featuring an alpha- or beta-hydroxyl substituent at C-5' of the carbocyclic ring is detailed. The starting point is the mandelate acetal 8. The overall strategy involves the stereocontrolled dihydroxylation of this dihydrothiophene, subsequent generation of the keto acetonide 12 followed by its Meerwein-Ponndorf-Verley reduction and beta-elimination, protection of the resulting dihydroxy thiaglycal, electrophilic glycosidation according to the Haraguchi protocol, reductive removal of the phenylseleno group, and end-game global deprotection. Acquisition of the alpha- and beta-5'-isomers is equally facile. Various 1D and 2D NMR techniques are used for assigning configuration.     

Reaction of Thiocarbonyl S‐Methylides with Acetylenic Dipolarophiles and an Unexpected Rearrangement of the Cycloadducts

The 1,3‐dipolar cycloaddition of 2,2,4,4‐tetramethyl‐3‐thioxocyclobutanone S‐methylide ( 2a ), generated in situ by thermal extrusion of N₂ from the corresponding 2,5‐dihydro‐1,3,4‐thiadiazole 1a , with electron‐deficient acetylenic compounds yields spirocyclic 2,5‐dihydrothiophene derivatives of type 4 (Scheme 2). Mixtures of diastereoisomers are obtained in the case of propiolates. The strained cyclooctyne also undergoes smooth cycloadditions with thioketone S‐methylides (Scheme 3). Under acidic conditions, the spirocyclic products of type 4 and 6a isomerize, via opening of the cyclobutanone ring and aromatization of the five‐membered ring, to thiophene derivatives of type 7 (Scheme 4).     

Ring inversion, structural stability and vibrational assignments of sulfolane c-C4H8SO2 and 3-sulfolene c-C4H6SO2

The structural stability of sulfolane (tetrahydrothiophene1,1-dioxide) and 3-sulfolene (dihydrothiophene1,1-dioxide) was investigated by DFT-B3LYP and ab initio MP2 calculations with 6-311+G**) basis set. The calculated symmetric ring-puckering potential of 3-sulfolene at the B3LYP level is consistent with a flat minimum that corresponds to a planar ring but at the MP2 level with a double minimum with a low barrier of about 193calmol(-1) to ring planarity in reasonable agreement with experimental results. From the calculations at the two levels of theory sulfolane was predicted to exist predominantly in the twist conformation. The vibrational wavenumbers were calculated at the MP2/6-31G** level of theory and the potential energy distributions PED among the symmetry coordinates of the normal modes were computed for the low-energy structure of the molecules. Complete vibrational assignments were provided on the basis of the calculated PED values. The experimental infrared and Raman spectra of the two molecules were compared to the calculated ones.     

Sulfur Monoxide Release and Capture: A Computational Study

Thermolysis of thiirane oxide leads to production of highly reactive sulfur monoxide. The liberated SO can in turn be trapped with a diene scavenger forming dihydrothiophene oxide. Since the intermediate diatomic possesses a triplet ground state, the SO transfer can proceed on two spin-state surfaces. Here, we study the competition between singlet concerted and stepwise triplet diradical mechanisms utilizing the M06-2X density functional as well as CCSD(T) and MRCI+Q wavefunction theories. We find that the decomposition of thiirane oxide prefers to pass through a triplet diradical intermediate that becomes accessible from a nearby minimum energy crossing point (MECP). Hence, the thermolysis of thiirane oxide is expected to predominantly release triplet ground state sulfur monoxide in agreement with previous experimental reports. The addition of ³SO to 1,3-butadiene initially generates an allylic diradical, that ring-closes to a thiirane oxide through another MECP, and a subsequent rearrangement gives access to the final product.     

Organocatalytic Asymmetric 1,6‐Addition/1,4‐Addition Sequence to 2,4‐Dienals for the Synthesis of Chiral Chromans

A novel asymmetric organocatalytic 1,6‐addition/1,4‐addition sequence to 2,4‐dienals is described. Based on a 1,6‐Friedel–Crafts/1,4‐oxa‐Michael cascade, the organocatalyst directs the reaction of hydroxyarenes with a vinylogous iminium‐ion intermediate to give only one out of four possible regioisomers, thus providing optically active chromans in high yields and 94–99 % ee. Furthermore, several transformations are presented, including the formation of an optically active macrocyclic lactam. Finally, the mechanism for the novel reaction is discussed based on computational studies.     

Regioselective hydroxylation of 2-hydroxychalcones by dimethyldioxirane towards polymethoxylated flavonoids

The flavone nucleus is part of a large number of natural products and medicinal compounds. In this presentation the novel regioselective hydroxylation of hydroxyarenes with DMD is described. The results showed further that flavonoids with 5-hydroxy group were selectively oxyfunctionalized at the para-position C8 carbon atom by DMD. Finally, according to this methodology, the naturally occurring isosinensetin, tangeretin, sinensetin, nobiletin, natsudaidain, gardenin B, 3,3′,4′,5,6,7,8-heptamethoxyflavone, quercetin and its derivatives were synthesized.