1.2- Thiazetidine 1-imines

Alkylidene sulfenes (75), generally prepared by the dehydrohalogenation of alkylsulfonyl chlorides, add readily to electron-rich multiple bonds. For example, with enamines, the thietane dioxide (e.g., 76) is formed diazoalkanes yield thiirane dioxides (episulfones) and imines (Schiff bases) afford 1,2-thiazetidine 1,1-dioxides. There are available numerous reviews of sulfenes, including cycloaddition reactions.102... 

Raasch, and Schaumann and co-workers, have studied the reactions of bis (trifluoromethyl)thioketene (83 R1 = CF3) with alkenes, with thioketones, and with carbodiimides or Schiff-base imines. The products were, respectively, thietans, 1,3-dithietans (84 R1 = CF3), and 1,3-thiazetidines (85 R1 = CF3) (from the carbodiimide).114,115 With phenyl azide the 1,2,3,4-thiatriazoline (86 R = CF3) is formed subsequent pyrolysis yields2,l-benzisothiazole.114... 

Fused 5-imino-l,2,4-dithiazolidine-3-thiones and 3-imines (100) take up nucleophiles on one sulfur atom, releasing the XCS structural unit of the heterocycle (Scheme 15) <85JCS(P1)1007>. Nonfused analogues (101) give up one sulfur atom to the nucleophile, the rest of heterocycle closing to form a 1,3-thiazetidine ring (102) (Scheme 16) <87ZC142>. 

Four-membered ring adducts from 2n + 2n cycloaddition of keten-imines to sulfur dioxide. Isolation of l,2-thiazetidin-3-one 1-oxides. jS-Sultames. Simple method for synthesis of substituted 1,2-thia-zetidin 1,1-dioxide. ... 

It has been reported that amines (32JCSH42) or imines (53JCS143), when reacted with formaldehyde and hydrogen sulfide, give rise to N-substituted 1,3-thiazetidines. However, in at least one case the structure was established to be an eight-membered ring dimer, which calls into question the structure of these compounds. 

Bis(trifluoromethyl)thioketene reacts with some imines to form 1,3-thiazetidines (78JOC2500). One derivative has been used by Dupont in surface treatment of water-repellent textiles (71USP3592811). 

P-Sultams.1 Reaction of 1 with imines and a base (usually pyridine) in THF results in 4-carbomethoxy-l,2-thiazetidine 1,1-dioxides (2) in 20-93% yield. All products have the trans-orientation. The N-unsubstituted P-sultams can be obtained by use of phenylselenenylethyl as the R group. This R group can be replaced by hydrogen in 70-90% yield by selenoxide elimination to an enamide, which is then treated with I2 and Na2S03.2... 

Some tricyclic 1,3-thiazetidines of type (51) are reported (95CPB63). Selective C-S bond cleavage of 3-aryl-fS-sultams (52) with ethylaluminium dichloride gives aryl ketones or aldehydes by a process involving 1,2-aryl shift, imine formation and hydrolysis of the imine (95TL245). 

Thiazetidine 1,1-dioxides (-sultams) are prepared by cyclization of appropriate precursors (e.g., Scheme 20) <1975BSF(2)807> or via [Z + Z cycloaddition of imines with sulfenes 32, generated in situ from the corresponding sulfonyl chloride and an organic base (Scheme 21) . 

Cycloaddition of sulfenes to Schiff bases (e.g., 434) and carbodiimides yields 1,2-thiazetidine 1,1-dioxides and 3-imino derivatives. A concerted mechanism was suggested. An earlier report of the cycloaddition of a sulfene to a Schiff base lacked proof for the structure of the adduct. Best yields are obtained with two equivalents of imine. The cis isomers can be converted to trans by treatment with triethylamine. ... 

Thioketenes, for example, 463, add to imines, carbodiimides, and azines to give 1,3-thiazetidines with exocyclic double bonds, as exemplified by the synthesis of 464. A novel ring contraction of 464a gives 1,3-thiazetidine 464b. 1,3-Thiazetidlnes are postulated as intermediates in the photochemical addition of thiobenzophenone to imines. They fragment to the two possible thiocarbonyl components and imines. ... 

Treatment of 3-amino-6-methoxypyridine or the corresponding thiourea 471 with thiophosgene gives the l,3-thiazetidine-2-thione 472. 1,3-Thiazetidine-2-thiones are possible intermediates in the reaction of carbon disulfide or isothiocyanates with isothioureas,in the reaction of carbon disulfide with imines, " and in the reaction of salts of dithiocarbamic acids with a,/3-unsaturated acid chlorides. 4-Imino-l,3-thiazetidine-2-thione is suggested as an intermediate in reactions of isothiocyanic acid (HNCS). ... 

The cycloaddition of isothiocyanates to imines gives 2-imino-l,3-thiazetid-ines, some of which are unstable.Cycloaddition of carbodiimines to bis(trifluoromethyl) ketene and isothiocyanates " gives 2,4-bis-imino-l,3-thiazetidines. The reaction of carbodiimides with 0,0-dimethyldithiooxalate to give 1,3-dialkyl-5,5-dimethoxy-2,4-imidazolidinedithiones... 

Alkoxycarbonyl isocyanates and isothiocyanates (216 X = O or S) in the presence of an excess of a benzylideneamine yield 2-acyliminoperhydro-l,3,5-thiadiazines (218). A two-stage process involving addition of the imine to the initially formed 1,4-dipolar 1 1-adduct (217), which in some instances is isolated as the ring-closed 1,3-thiazetidine, is likely (Scheme 35) (83CB1297, 85CB4196). 

The aza-Corey-Chaykovsky reaction yields aziridines via the interaction of oxosulfonium or sulfonium ylides with imines. The reaction mechanism has not been established, and no intermediate has been observed or isolated. The fact that stable thiazetidine 140 fragments thermally into aziridine 141 and suMnate ester 142 supports the hypothesis that the aza-Corey-Chaykovsky reaction proceeds via such a four-membered ring intermediate formed by [2 -F 2] cycloaddition. ... 

Although neither the use of triphosgene nor of oxalyl chloride afforded the desired amido chlorides, the thiazetidinone has been found [561] to be a highly versatile intermediate allowing the facile conversion of thioureas into either carbo-diimides or isoureas in good yields. 3-(4-Fluorophenyl)-l,3-thiazetidin-4-one-2-(4-fluorophenyl)imine 770 was obtained in 63% yield as the main product from the reaction of N,N -bis(4-fluorophenyl)thiourea 769 with one-third of an equivalent of triphosgene. 

Heating the 3-(4-fluorophenyl)-l,3-thiazetidin-4-one-2-(4-fluorophenyl)imine 770 either neat or in refluxing toluene affords the expected carbodiimide 771 [562] as the sole product (presumably with evolution of 0=C=S). 

Thiazetidines and their Derivatives.—Cyclization reactions yield (140) from benzenesulphonyl isocyanate and a thioamide, (141) from aroyl isothiocyanates and DCCI, (142) from dihydroisoquinoline and the CSj adduct of a Wittig reagent,and (143) from the BF3 EtjO-catalysed reaction of ethylenethiourea and aryl aldehydes. Thiazet (144) reacts with SbjTcs, presumably through the open thione-imine form, to give (145). 1,3-Thiazetidines have been proposed as intermediates. ... 

In the generation of t-butyl(cyano)thioketene at low temperature in the presence of imines, addition across the C=S bond occurs to give thiazetidine derivatives, while at higher temperatures /3-thiolactams are obtained . 

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