Dithianes olefination

Total synthesis of macrolide immunodepressants using 1,3-dithiane aldol couplings and a-bond olefin constructions 98ACR35. 

The addition of thioketones to olefins is very interesting indeed. Unsubstituted electron-rich olefins yield 1,4-dithianes as final products(112) ... 

Olefins analogous to 158 and 159 were also isolated from the CuS04-catalyzed decomposition of ethyl diazoacetate in the presence of 2-isopropenyl-2-methyl-1,3-dithiane (total yield 56%, E Z — 4 1) a butadiene was absent from the reaction mixture 161). With dimethyl diazomalonate instead of ethyl diazoacetate, only the Z-olefin resulting from a [2,3]-sigmatropic rearrangement of the corresponding sulfur ylide was obtained in 36 % yield 161). When the same procedure was applied to... 

Studies with other thiocarbonyl compounds reveal a different reactivity pattern from that of thiones in the presence of olefins. 0-Alkyl thiobenzoates do not form dithiane products. Instead, if an olefin carries no bulky substituents, the intermediate diradical cyclizes directly to the thietane ring (Eq. 4). The excited (n, 71 ) state of thiophosgene reacts with alkenes to... 

The same group has also reported the use of dithiane functionalized olefinic aldehydes in an intramolecular process. Treatment of 289 with the secondary amine 290 led to the formation of the intermediate ylide 291, which delivered a range of tricyclic products (292) in high material yield as essentially a single stereoisomer after in situ cycloaddition (Scheme 3.95). 

With Dithiane. Dithiane is one of the most popular functionalized carbanion used for the ring opening of epoxides. This reaction has been studied by different groups [31,56], The anion of bis(phenylthio)methane has been successfully used for the opening of epoxides derived from furanose [56]. This method is an excellent way to prepare formyl derivatives that are suitable for chain extension by olefination. Alternatively formyl derivatives can be reduced to hydroxymethyl derivatives. A recent application of epoxide 33... 

Under the optimum reaction conditions, reactions of the 2-stannyl-1,3-dithiane derivatives 16,18,19 with various olefinic compounds were carried out and the results are shown in Table 3. 

Table 3. Reactions of 2-Stannyl-l, 3-dithiane Derivatives (16,18, 19) with Various Olefins...

Ketene dithioacetals, available by the Peterson olefination of 2-trimethylsilyl-l,3-dithiane with aldehydes and ketones, are oxidised to the /rara-l,3-dithiane 1,3-dioxides 44 with virtually complete diastereo- and enantioselectivity using Sharpless methodology <03JOC4087>. 

Interesting examples of optical resolutions include the use of dicarbonyl-rhodium(i) 3-trifluoroacetyl-(li )-camphorate for g.l.c. separation of chiral olefins and of dimeric nickel(ll) bis-(3-trifluoroacetyl-li -camphorate) for an improved separation of chiral epoxides (cf. Vol. 8, p. 8). The resolution of (i /5)-pantoic acid with chiral amines derived from a- and jS-pinene (Vol. 7, p. 43, ref. 420) may signal their more widespread use. 1,3-Dithian 1-oxide has been resolved. ... 

The ionic stability of phenyl selenides can also be advantageous in the choice of addition reagents. Reagents serving as precursors to heteroatom-stabilized radicals are more accessible because of the poorer leaving group ability of the phenylseleno substituent, as shown in Scheme 18. Phenylseleno precursors to captodative radicals have been shown to be ambiphilic in nature, with successful additions to electron-rich as well as electron-deficient olefins [54], The stable precursor to a highly nucleophilic radical, 2-phenylseleno-l,3-dithiane has been shown to add to electron-deficient olefins [55]. 

Barton olefinations, 35 Eschenmoser s sulfur extrusion, 59-60, 261 ThioacCtals. See 1,3-Dithianes 1,3-Dithiolanes ... 

The preparation of the C33-C35 segment [137] began with the Horner-Emmons olefination of wo-butyraldehyde, reduction, and asymmetric epoxida-tion [39] leading to epoxy alcohol 234 (Scheme 33). Dithiane epoxide ring opening (regioselectivity 12 1), primary alcohol reduction, and secondary alcohol protection completed the synthesis of this segment ( 235). 

The Reformatskii synthesis with trimethylsilyl esters leads directly to / -hydroxy acids after acidic work-up The latter can be converted into olefins via / -lactones with retention of the initial geometry and without double bond isomerization. The synthesis of oxo compounds through 1,3-dithianes has been applied to a convenient preparation of a-keto esters... 

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