Thiocarbonate cyclic

On reaction of the S/Z-mixture 746 with benzylamine in the presence of CS2, the cyclic thiocarbonates 757 and 758 are formed by attack of benzylammo-nium thiocarbonate on 747, N,N -thiourea 759 is also formed [236] (Scheme 5.81). 

A 1,3-oxathiolane derivative (100) is formed when 2-mercaptoethanol is carbonylated by nickel carbonyl in pyridine (Scheme 118).181 It is probable that the mechanism involves carbonyl insertion into the Ni—S bond of intermediate thiolatonickel complexes and it is significant that compounds in this category (cf. 101,102) can be transformed into the cyclic thiocarbonate by treatment with carbon monoxide (Scheme 118).181... 

Cyclic thiocarbonates, such as compound 169, react smoothly with allylmagnesium bromide. Careful control of the reaction conditions allows monoalkylation. Trapping of the intermediate sulfur anion with Mel provided the 1,3-dioxane in 78% yield (Equation 20) <2003H(59)87>. 

Conversion of 1,2-diols to alkenes. The cyclic thiocarbonate is available from reaction of the diol with thiophosgene or thiocarbonyldiimidazole, and reacts with added trimethylphosphite via a -elimination to the alkene. 

The Corey-Winter procedure was used to obtain the cyclic thiocarbonate 206 from the corresponding vicinal diol <2000EJ0939>. 

Cyclic thiocarbonates offer another class of substrates for radical deoxygenation (Scheme 3.9b). In particular, thiocarbonates formed from a diol derived from a primary and secondary hydroxyl are of particular interest, since they can be deoxygenated regioselectively with tributyltin hydride and AIBN.53 In these cases, the secondary position is deoxygenated owing to the higher stability of secondary over primary radicals. As expected, radical reduction of thiocarbonates derived from two secondary hydroxyls leads to a mixture of deoxygenated isomers.52b 53... 

Vicinal syn- and aufi-diols, as shown in Figure 4.42, can be prepared diastereoselectively (cf. Figures 8.10,8.13-8.15,8.32). In the Corey-Winter process they are first converted into cyclic thiocarbonates (cf. Section 6.4.4 for a similar reaction mechanism). Upon heating in trimethyl phosphite, these thiocarbonates furnish olefins. In what is evidently a one-step reaction, phosphorus and sulfur combine with one another and the five-membered heterocycle fragments. C02 is released and the olefin results from a xyu-elimination. Because of the latter, a syu-diol gives the trans-oieim and an anti- diol gives the cw-olefin in the Corey-Winter sequence. 

Monodeoxygenation of 1,2- and 1,3-diols was achieved via their cyclic thiocarbonates, prepared from the diol and A/,A/ -thiocarbonyldiimidazole, by reaction with BusSnH-AIBN followed by alkaline hydrolysis (presumably, F would also be effective for the cleavage step). Equation (14) shows this process applied to synthesis of a derivative (73) of 5-deoxyglucose. Exclusive secondary deoxygenation is expected on the basis of radical stability in contrast, the derivative (72) was readily converted by an ionic process to an intermediate suitable for 6-deoxygenadon, since treatment with KI gave (74) quantitatively. 

The di-O-tosylates (prepared by action of tosyl chloride in pyridine) are reduced with zinc (Nal/Zn route e Tipson-Cohen reaction) [13]. Cyclic ortho-esters (prepared by reaction of the diol with ethyl orthoformate) are transformed into olefins by simple heating in the presence of acids (Eastwood reaction, route b) [14]. Cyclic thiocarbonates (obtained by reaction of a diol with thiophosgene or (V,(V -thiocarbonyl-di-imidazole) are reduced to olefin with trimethyl phosphite (Corey-Winter method, route c) [15]. Finally, reduction of vicinal di-xanthates with tri- -butyltin hydride according to the Barton procedure [16] affords olefins via a reductive elimination process route a). The Corey-Winter, Garegg, and Tipson-Cohen methods are most commonly applied for deoxygenation of sugar diols. 

Epoxy-17a-pregnan-20-ones react with pyridine thiocyanate to give thiocyano-alcohols, which readily cyclize to afford cyclic thiocarbonates (51). ... 

Diol 164 was treated with l,l -thiocarbonyldiimidazole to produce the cyclic thiocarbonate (168) product in 67% yield over two steps from salvinorin A (Scheme 26) [49]. Unfortunately, these conditions were found to cause epimerization at C-8, the products of which were inseparable on silica gel. However, this meant that initial separation of the C-8 epimers of the c/s-diol starting material was not necessary. Radical reduction (tributyltin hydride, AIBN, toluene, 80 °C) of the epimeric thiocarbonate mixture afforded the separable C-l deoxy products in 47% combined yield. Subsequent acetylation of the C-2 hydroxyl under standard conditions (Ac20, pyridine) gave 1-deoxysalvinorin A (169) in 82% yield. 

This ring is formed by reaction of neighbouring hydroxy and lactam thiocar-bonyl groups with carbonyldi-imidazole and sodium imidazolide (Naim) at or below room temperature. The product is a cyclic thiocarbonate which acylates amines under mild conditions. 

The first stage of the process consists of refluxing the glycol with 1,1 -thiocarbonyldi-imidazole for 30 min 48 the resulting cyclic thiocarbonate is converted into the olefin by 70-80 hours refluxing with an excess of trimethyl phosphite. In this way, for example, cis-stilbene was obtained in 92% yield from meso-hydrobenzoin, and trans-cyclodecene in 81 % yield from trans-1,2-cyclodecanediol. 

The second step, involving the reaction of the cyclic thiocarbonate intermediate formed above with trialkylphosphite, is of great interest. The phosphite P attacks the S of the thio-carbonyl group, generating a cyclic dialkoxycarbene, as shown below ... 

Benzyl, 2,3-thiocarbonate Benzyl 4-0-benzyl-6-deoxy-fl-i.-mannopyrano-side cyclic thiocarbonate, SCI. Benzyl 4-O-benzyl-p-L-rhamnopyranoside 2, 3-thiocarbonate... 

Benzyl 4-0-benzyl-6-deoxy-p-L-mannopyranoside cyclic thiocarbonate, B-20... 

Benzyl 4-0-benzyl-2,3-0-ex o-benzylidene-a-L-rhaimiopyranoside, B-20 Benzyl 4-0-benzyl-2,3-0-emfo-benzylidene-a-L-rhamnopyranoside, B-20 Benzyl 4-0-benzyl-6-deoxy-p-L-mannopyranoside cyclic thiocarbonate, SCI, B-20... 

Monodeoxygenation of the aminodiol 1159, previously protected as thiocar-bonate 1160, thereby affording 1161 has been reported [411]. Compound 1159 was reacted with thiocarbonyldiimidazole SCDl to give the cyclic thiocarbonate 1160 in 70% yield. 

The introduction of the tetrahydrofuranyUdene butenoUde unit was achieved starting with the addition of the lithium anion of 4-methoxy-3-methyl-2(5//)furanone (241) (Scheme 22), followed by acid cleavage to provide lactol 254 which was oxidized with an excess of o-iodoxybenzoic acid (IBX) in DMSO to yield 255. Condensation with thiophosgene at —50°C provided a 3.5 1 mixture of cyclic thiocarbonates 256 and 257 as a 68% yield, the ratio depending on the reaction temperature. Finally, thiocarbonate 256 was converted to ( + /—)-didehydrostemofoline (52) in 66% yield after treatment with trimethyl phosphate at 120°C, while ( + /—)-isodidehydrostemofoline was isolated in 64% yield from thiocarbonate 257. 

A new mild reaction for the deoxygenation of secondary alcohols has been applied successfully to sugars the reaction, which is radical in character, involves the reduction of a thiobenzoate with tributylstannane (see Scheme 25). Other references to the use of thioesters and the photochemical transformation of dithiobis(thioformates) into thiols are reported in Chapter II, the reaction of cyclic thiocarbonates with methyl iodide to give tu-iodo-iS-methyl thiocarbonates... 

The reaction of cyclic thiocarbonates with methyl iodide (Chapter 13) and the use of 5 -deoxy-5 -iodo-nucleosides in the synthesis of unsaturated nucleosides (Chapter 14) are reported elsewhere. 

Some cyclic thiocarbonates derived from carbohydrate 1,2-diols undergo O - ... 

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