Dithianyl Anions

Reactions.—1,3-Dithianyl Anions. 1,3-Dithianyl anions continue to find wide-ranging utility in the synthesis of diverse structures, including 2-deoxy-L-lyxose derivatives, eburnamine precursors, l,2-diformyl-6,6-dimethylcyclohex-2-en-l-ol, cannabinoids, tertiary acyloins, cyclitols, unsaturated carboxylic acids, the terpenes egomaketone and a- and jff-curcumene, (205)-20-hydroxycholesterol, norpyrenophorin, pyrenophorin, and vermiculine, compounds with chiral methyl groups, (+)-rrans-burseran, enones, the macrocyclic lactam A-methylmaysenine, olivin, macrocyclic acetylacetone crown ethers, [5.1]metacyclophane, ( )-laurencin, monosaccharides, y-keto-esters and their precursors, muscarine analogues, quinols, epi- 

Furuhata, H. Takahashi, and Y. litaka, Chem. Pharm. Bull., 1978, 26,2782. 

7-hydroxymyoporone, butyrolactones, and -diketone enol ethers. A novel synthesis of (rf,0-muscone (31) involves a two-carbon ring-expansion process. 2-Lithio-2-trimethylsilyl-l,3-dithian reacts with sulphur dioxide in a Wittig-like reaction to give the appropriate sulphine (see also Chap. 3, Pt II, p. 160, and Vol. 5,p. 133).  

3- dithian, which is the y-phenyl analogue of (34), has been found to undergo substitution at the a-position with hard electrophiles [e.g. D+, McjSiCl, and (Me0)2S02l and at the y-position with softer electrophiles e.g. RI and RBr). 2-Alkylidene-l,3-dithians can be prepared through the reaction of 2-lithio- 

3- dithians with 2,2 -dipyridyl disulphide. An example of an intramolecular Michael addition to a 2-alkylidene-1,3-dithian (35) has been described.  

Reactions.—, i-Dithianyl Anions. The Corey-Seebach 1,3-dithianyl anion rates as one of the most popular sulphur anions and nucleophilic acylating agents, as demonstrated by its recent use in the syntheses of potential precursors of the macrocyclic antitumour agent maytansine, of cyclopentenones and other unsaturated ketones,of octoses, of lla-hydrox)rprogesterone, of deuteriated aldehydes, of alnusone, of the sex-attractant of the Douglas fir tussock moth, of l,4-diketones, of 3-s-butylglutaraldehyde, of linaloyl 

Gateau-Olesker, S. D. Gero, C. Pascard-Billy, C. Riche, A.-M. Sepulchre, G. Vass, and 

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Since neither direct acylation of the 2-position of oxazole 15 (Ha) nor acylation of the 1,3-dithianyl anion (Hb) was observed, the products were rationalized as arising through selective C-acylation of the ring-opened tautomer 15c. 

Intramolecular 1,3-dipolar additions of nitrones and nitrile oxides to carbohydrate alkene groups have met with success. Thus, treatment of the unsaturated heptose ether 68 (Scheme 17), which can be made following 1,3-dithianyl anion addition to C-l of 2,3,4-tri-0-benzyl-5,6-dideoxy-D-xy/o-hex-5-enose, with IV-methylhydroxylamine in refluxing methanol, affords the nitrone 69 that cyclizes to give the bicyclic isoxazolidine 70 (60% isolated) together with the epimer at the new asymmetric center carrying the methylene carbon atom (16% isolated) [35]. 

The same study shows that with the complex of A W-dimethyl-o-toluidine (38), the selectivity depends on time, temperature and the nature of the anion (Table 4 and equation 34).87 Again, equilibration occurs with the tertiary nitrile-stabilized anion, favoring the C-4 substitution product, while lithioacetonitrile favors addition at C-3. The 2-methyl-1,3-dithianyl anion gives precisely the same product mixture at -78 °C and at -30 C there is no evidence for equilibration with this anion. 

Regiocontrolled Corey-Seebach s epoxide ring-opening with 1,3-dithianyl anion... 

Regioselectivity in o-disnbstitnted arenes is often high and nseful. A series of examples is snmmarized in Figure 4. The resonance donor substitnent (OMe) appears to dominate the directing inflnences, favoring addition at the less-hindered position meta to itself Bnt with two identical substituents, the addition is preferred in the adjacent position. For example, with the complex of benzocyclobutene, six carbon nucleophiles were tested and each gave addition exclusively at C-3. With the complex of indan, selective addition at C-3 was observed with dithianyl anions, but cyano-stabilized... 

Numerous synthetic applications have been described using 1,3-dithianyl anions [133]. For instance, the lithium compounds 2 undergo nucleophilic additions with oxiranes and with carbonyl compounds ... 

Attempts to effect the direct addition of 2-lithio-l,3-dithian to 17-keto-steroids have met with limited success. On the other hand, reactions of 17-spiro-epoxides were found to provide convenient access to homopregnane derivatives. Whereas treatment of the 17-ketoandrostene (188) with dimethylsulphoxonium methylide gave an inseparable mixture of the two epimers (189) and (190), reaction of (188) with dimethylsuphonium methylide afforded exclusively the 17j3-oxiran (189) in high yield. Opening of the epoxide of (189) with 2-methyl-1,3-dithianyl anion proceeded smoothly to give the 17)S-hydroxy-dithian (191). 

The anions, generated in situ by desilylation of silylacetylenes, allylsilanes, propargylsilanes, a-silyloxetanones, bis(trimethylsilylmethyl) sulfides, and other silane derivatives,can undergo nucleophilic addition to ketones and aldehydes (eq 11). Al-(C,C-bis(trimethylsilyl)methyl) amido derivatives can add to aldehydes followed by Peterson alkenation to form acyl enamines. Treatment of 2-trimethylsilyl-l,3-dithianes can generate dithianyl anions, which are capable of carbocyclization via direct addition to carbonyl or Michael addition (eq 12). The fluoride-catalyzed Michael additions are more general than Lewis acid-catalyzed reactions and proceed well even for those compounds with enolizable protons and/or severe steric hindrance (eq 13). ... 

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