Cycloaddition reactions of thiocarbonyls

Table 14 Cycloaddition Reactions of Thiocarbonyl Compounds with Dienes...

Cycloaddition Reactions of Thiocarbonyl S,5-Dioxides and Related Sulfur(VI) Compounds... 

The dipolar 1,3-cycloaddition reaction of thiocarbonyl ylides to thiones can be a source of 1,3-dithiolanes. Its regioselectivity depends on the nature of substituents in the substrates. Thus, the. J-methylide 589, generated in situ by thermal decomposition of the corresponding l,5-dihydro-l,3,4-thiadiazoles, was reacted with the trithiocarbonate 588 to give a labile 4,4,5,5-tettasubstituted-l,3-dithiolane 590, which easily isomerized to an open-chain compound 591 in the presence of acids in solution (Scheme 84) <2000EJ01695>. 

Rao, V. R, Chandrasekhar, J., Ramamurthy, V., Thermal and Photochemical Cycloaddition Reactions of Thiocarbonyls A Qualitative Molecular Orbital Analysis, J. Chem. Soc., Perkin Trans. 2 1988, 647 659. 

Thiocarbonyl S-imides are excellent dipols in [3+2] cycloaddition reactions. Also [2+4] cycloaddition reactions of thiocarbonyl -imides are known. 

When planning reactions of thiocarbonyl compounds with electrophilic carbene complexes it should be taken into aceount that thiocarbonyl compounds can undergo uncatalyzed 1,3-dipolar cycloaddition with acceptor-substituted diazomethanes to yield 1,3,4-thiadiazoles. These can either be stable or eliminate nitrogen to yield thiiranes or other products similar to those resulting from thiocarbonyl ylides [1338]. 

For preparative purposes, the reaction of thiocarbonyl ylides with carbonyl compounds can be considered as an alternative method for the synthesis of 1,3-oxathiolanes. Aromatic aldehydes, chloral, glyoxalates, mesoxalates, pyruvates as well as their 3,3,3-trifluoro analogues are good intercepting reagents for thioketone (5)-methylides (36,111,130,163). All of these [3 + 2] cycloadditions occur in a regioselective manner to produce products of type 123 and 124. 

Reactions of thiocarbonyl ylides with nitriles are scarce. Simple nitriles do not undergo bimolecular cycloaddition (171). There is, however, a single example of an intramolecular case that was reported by Potts and Dery (24c,62). By analogy to the intramolecular cycloaddition with acetylenic dipolarophiles (Scheme 5.40), the primary product derived from the reaction of a thiocarbonyl ylide with a nitrile group undergoes a subsequent elimination of phenylisocyanate to give the fused 1,3-thiazole (131). 

A cycloreversion mechanism is suggested for the transformation of the nonisolable cycloadduct 90 to the aldehyde 91 and isothiocyanate 92 <1996BCJ719> and for the spiro-1,4,2-oxathiazole intermediates 94 to the dioxothiazoline 95 and the aryl isothiocyanate 92 <2001MOL510>. Both cycloadducts are obtained by cycloaddition reactions of nitrile oxides 88 to thiocarbonyl compounds (Scheme 12). 

Huisgen and co-workers reported, in three papers (02T507, 02T4185 and 02HCA1523> the conversion of various 1,3,4-thiadiazolines 86 into thiocarbonyl ylides 87 via extrusion of N2. They then described cycloaddition reactions of these ylides 87 with various a,P-unsaturated esters and nitriles and postulated reaction mechanisms for the regioselectivity and stereochemistries observed in the transformations. 

The cycloaddition reaction of chiral thiocarbonyl 5-oxides derived from terpene alcohols such as (—)-menthol, ( —)-borneol, (+)-a-fenchol and (—)-3-tWo-hydroxy-2-CTitfo-phenylbornane affords 2-substituted 2-alkoxysulfonyl-3,6-dihydro-4,5-dimethyl-2//-thiopyran 1-oxides IIA and 11B as a mixture of diastereomers85. 

In contrast, the cycloaddition reaction of ( )- or (Z)-lO-chloro-lO-thioformylcamphor S-oxide with 2,3-dimethyl-1,3-butadiene proceeds with complete asymmetric induction and affords in each case a single diastereomer 12 or 13 only differing in the reaction rate the (L)-thiocarbonyl 5-oxide reacts faster than the (Z)-isomer85. 

The cycloaddition reactions of ketenimines to thiocarbonyl groups to give both 1,2-(iminothietanes) and 1,4-adducts have been reviewed. The frontier molecular orbitals of the reactants are important for the addition that is classed as a ( 2 + 2a) process. Steric factors play a role and the rate of 1,2-addition to give 2-iminothietanes depends more on the substituents at the terminal carbon atom of the ketenimine than 1,4-addition to give a six-membered ring. The rate of 1,2-... 

Nitrosoalkenes act as heterodienes in cycloaddition reactions with thiocarbonyl compounds to afford the first examples of the 4H-1,5,2-oxathiazine ring system (152) in high yields (60-99%), and the low-temperature cycloaddition of dioxadithiazine tetroxides to... 

A review of recent developments in synthetic organic sulphur chemistry included much valuable material pertinent to cyclic sulphur compounds, and another review covered photocycloaddition reactions of thiocarbonyl compounds with olefins to give 1,4-dithians and cycloadditions with dienes to give thian derivatives. Macrocyclic polythioethers and their complexes have been reviewed, and in other articles the conformational aspects of multisulphur heterocycles, sulphur-containing [2,2]metacyclophanes, and other cyclic sulphur compounds have been discussed. Other reviews mention configurational aspects of cyclic sulphur compounds. ... 

Two papers reporting on cycloaddition reactions of dithio-esters have appeared. Smutny and his co-workers obtained 2/f-thiopyrans (279) from the reaction of methyl 3-(dialkylamino)dithioacrylate with maleic anhydride. They interpreted the reaction in terms of an initial nucleophilic attack of the thiocarbonyl sulphur atom on the electrophilic double bond of the anhydride, forming the intermediate (280), and a subsequent... 

Adamantanethione was also used as a dipolarophile to trap 26, and the [3+2] cycloadduct is obtained in 81 % yield. Cyclooctyne is also used as a dipolarophile for trapping diphenylthiocarbonyl S-sulfide and p-chlorodiphenylthiocarbonyl 5-sulflde. The [3+2] cycloaddition reaction of the thiocarbonyl 5-sulflde 30 with diarylsulfides... 

Reaction of lithium trimethylsilyldiazomethane (TMSC(Li)N2) with thiocarbonyl compounds has proved to be a convenient method for the preparation of 5-substituted 1,2,3-thiadiazoles. This reaction is very similar to the Pechmann-Nold reaction but probably does not proceed through a dipolar cycloaddition pathway. A number of examples of this type of reaction were described in CHEC-II(1996). More recently, it was reported that TMSCN2Li also reacts with diethylaminothiocarbonyl chloride to afford a mixture of 1,2,3-thiadiazoles 66 and 67 (Equation 19) <1997BSB533>. 

Scheme 12 shows synthesis of 1,2,3-thiadiazoles by the Wolff, Hurd-Mori and Pechmann-Nold methods. Pechmann s and Wolffs are the oldest of the methods. The Pechmann-Nold synthesis involves the [3 + 2] cycloaddition of diazo-compounds to isothiocyanates or thiocarbonyl compounds (modified Pechmann synthesis). The use of thiocarbonyl compounds in the [3 + 2] cycloaddition step has broadened the scope of this reaction and made the starting materials more readily accessible. Wolffs method requires the synthesis of diazoketones that are treated with a thionating reagent to produce 1,2,3-thiadiazoles. With the development of new methods of diazotransfer reactions, the diazoketone precursors have become easily attainable and with further attention to the thionating reagents, this reaction is also useful for the synthesis of 1,2,3-thiadiazoles. 

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