1,3-Dithianyl derivative

One carbon atom elongation procedure has been developed by Knowles [81]. It was performed via acylation of 1,3-dithianyl derivative... 

Substitution m- to the methoxy group, established earlier for arene/chromium tricarbonyl systems (ref. 119), has been used to prepare the 1-(2-dithianyl) derivative of estrone (ref.120). A solution of 2-lithio-1,3-dithian in tetrahydrofuran at -78°C treated with the chromium tricarbonyl complex of HO-protected estrol (from the protected steroid with chromium hexacarbonyl by refluxing in... 

Aldehydes are generally accepted to be soft electrophiles towards allyl anions such as (82), and usually lead to good yields of y-adducts. However, with dithianyl derivatives, e.q. (84), the exposed nature of the a-site results in an increased level of reaction via this site. This may be suppressed if the normal lithium counterion is replaced by cadmium. The resulting organometa11ic complex gives good levels of y-selectivity with aldehydes (Scheme 28). The same authors have also studied the effect of added CdCl, to anions derived from a,B-unsaturated esters (85). The influence of an adjacent to... 

The value of the 1,3-dithian route to branched-chain sugar derivatives has been illustrated further by stereospecific syntheses of 3-C-formyl, 3-C-hydroxymethyl, and 3-C-methyl derivatives of D-psicose from the ketone (373) via the dithianyl adduct (374). Addition of nitromethane to (373) gave both 3-C-nitromethyl-o-psicose and -fructose derivatives, which, after separation by chromatography, were reduced to the corresponding 3-C-aminomethyl derivatives. The use of dithianyl derivatives in the synthesis of streptomycin components is dealt with in Chapter 18. 

An efficient synthesis of ( )-quebrachamine is based on the construction of a suitable precursor via ring cleavage of an a-diketone monothioketal (810) (80JCS(P1)457). This monothioketal, available from 4-ethoxycarbonylcyclohexanone ethylene ketal, was fragmented to the dithianyl half ester (811) with sodium hydride in the presence of water. Reaction of (811) with tryptamine and DCC provided an amide which was converted to the stereoisomeric lactams (812) on hydrolysis of the dithiane function. Reduction of either the a- or /3-ethyl isomer with lithium aluminum hydride followed by conversion of the derived amino alcohol to its mesylate produced the amorphous quaternary salt (813). On reduction with sodium in liquid ammonia, the isomeric salts provided ( )-quebrachamine (814 Scheme 190). 

Ketene derivatives S,S-Acetals and ketals Diphenyl-2-(l,3-dithianyl)phosphine oxide, 126... 

Preparation (2,182, ref. 1). The procedure has now been published.1 Reaction with steroid oxides. 2-Lithio-l,3-dithiane reacts with 5a-cholestane-2a,3a-oxide (1) to give the 2/3-dithianyl-3 -hydroxy derivative (2). Desulfuriza-... 

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). 

Nitrobenzene and many of its 2-, 3-, and 4-substituted derivatives are converted into nitroaniline derivatives by treatment with sulfenamides in the presence of t-BuOK (eq 90). In this conversion, termed vicarious nucleophilic substitution (VNS), the base presumably promotes both the formation of the nucleophilic sulfenamide anion and the -elimination of the thiocar-bamoyl group from the other examples of t-BuOK-promoted VNS reactions of nitrobenzenes have appeared in recent years. An interesting example of this process involves the synthesis of dithianylated nitrobenzenes which are hydrolyzable to aldehydes (eq 91). The treatment of mixtures of m-nitroaniUne and enoUzable ketones with t-BuOK in DMSO leads to nitroindoles by oxidative nucleophilic substitution of hydrogen (eq 92). The proposed mechanism for this transformation involves attack of the potassium enolate of the ketone on the ring, spontaneous oxidation of the a-adduct, and imine formation and tautomerization. 

Anhydromaltose has been converted to the pseudo-disaccharides (25) containing 3-amino-3-deoxy-epz-inositol or 1-amino-l-deoxy-l-L-myo-inositol via the 6-deoxy-6-nitromaltose derivative (26). The branched-chain unsaturated 6-nitro-sugar (27), prepared conventionally from D-glucose, yielded isomeric dithianyl adducts which were similarly cyclized to give the nitro-cyclitols (28) and (29), of interest as potential intermediates for the synthesis of tetrodo-... 

A wide range of functional groups within the ketone are tolerated, including heterocyclic- [857, 858], fluoro- [859-862], chloro- [863], bromo- [864], perfluoro-alkyl- [865], cyano-, azido-, nitro- [866-868], hydroxyl- [869, 870], sulfur-[871-873], and dithianyl groups [874]. Even organometallic derivatives [875, 876], such as sUyl- [877] and germyl groups [878] are accepted. 

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-... 

In an approach to tetrodotoxin, the triol (25), derived from D-glucose as for the dithianyl analogue (see Vol. 14, p. 149-150), has been converted to the more advanced intermediate (26) 9... 

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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