1.3- Dithiole-2-phosphonates

The 1,3-ditelluretane 88 is obtained as a minor product along with the 1,3-ditellurafulvene 89 by the reaction of phenylacetylide with tellurium followed by acidification with trifluoroacetic acid (Scheme 27) <2003TL2397>. In the reaction of trimethylsilylethynyl tellurolate, use of tifluoroacetic acid in /-butyl alcohol at — 20°C leads to the formation of the 1,3-ditelluretane 90, presumably via the telluraketene 91. Vilsmeier-Haack reaction on the crude ditelluretane 90 furnishes dialdehydes 27 and 92 in 10% yield. 1,3-Ditelluretanes 27 and 92 can be transformed into other derivatives, as shown in Scheme 28. An /. // mixture of 27 and 92 condenses smoothly with phosphorane to give diester product 93. The reaction with diesterdithiole phosphonate or dithiole phosphonate affords 1,3-ditelluretane derivative 94 or 95, respectively. 

The reaction of trialkyl- and triaryl-phosphines with 1,3-benzodithiolylium salts leads to formation of phosphonium salts which are deprotonated by treatment with n-butyllithium to produce (69). The similar reaction of trialkyl phosphites in the presence of sodium iodide yields dialkyl phosphonates which can be deprotonated to (70). Both (69) and (70) can react further with ketones to give the 2-alkylidene-l,3-dithiole derivatives (71) (80AHC(27)151>. The ylide (72) has also been prepared (80H(l4)27l>. 

Reduction of the iminium salt 172 with NaBHa led to formation of the 4-methyl-l,3-dithiole derivative 173, which upon treatment with AC2O, HPE, and then Nal afforded 174, then reacted with triethyl phosphite to form the phosphonate 175 (Scheme 18) <2000EJ051>. 

Conjugated yne-2-ynylidene 1,3-dithioles 228 were synthesized via Wittig reactions of phosphonium salts 225 with 3-phenyl-substituted propargyl aldehydes 227 (R = H, = Ph). Diaryl-substituted derivatives 228 were prepared in Horner-Wittig reactions of phosphonates 226 with ketones 225 (R =R = Ph or -02NC6H4) (Equation 13) <2004CL1190>. 

The Horner-Wittig reaction of the carbanion generated from the phosphonate 232 with 2,5-diformylthiophene 233 afforded 1,3-dithiole derivatives 234 (Equation 15) <1997TL6107>. 

The 7t-extended 1,3-dithiole 237 containing a cycloproparene moiety was synthesized in the Horner-Wittig reaction involving the phosphonate carbanion derived from 235 and the benzoyl-substituted cycloproparene 236 (Equation 16) <2004EJ0138>. 

It was found that carbanions 241 derived from mono- or unsubstituted diethyl l,3-dithiol-2-yl phosphonates 240 existed in an equilibrium with open forms 242 which could dimerize to dianions 243 followed by protonation to give 244 as a cisItrans-vcix-KlVim (Scheme 28). This reaction sequence was responsible for the low-yield synthesis of unsymmetrically substituted TTFs <1999TL7219>. 

Other examples of functionalization at C-2 via phosphorus ylides and phosphonate carbanions are described in Section 4.12.11. Utilization of 2-non-phosphorus-containing carbanions was also exemplified. Thus, 2-silicon-substituted 1,3-benzodithioles were synthesized via deprotonation of benzo-l,3-dithiole 245 with -BuLi and subsequent treatment of the resulting anion with trimethylsilyl chloride (TMSCl) to give 2-(trimethylsilyl)-benzo-l,3-dithiole 246 (Scheme 29). The second silyl group was introduced by further deprotonation of 246 ( -BuLi) followed by the reaction with an additional equivalent of TMSCl. Tin-substituted benzo-l,3-dithioles were synthesized in a similar way but the deprotonation of the monostannyl derivative was carried out with LDA (Scheme 29) <1996CL171>. 

Synthesis of fused D-A systems such as 665 involved /-butyldiphenylsilyl protection of 4,7-dihydroxy-l,3-benzo-dithiole-2-thione 661, then the Horner-Wittig reaction of the resulting 662 with the carbanion derived from phosphonate 663 and finally deprotection of the TTF 664 to the required 665, obtained as green crystals (Scheme 94) <2003AG2871, 2004JOC2164>. 

In the reaction of l,3-dithiol-2-yl-phosphonate 678 with 679, the corresponding unsymmetrically substituted TTF derivative 680 could be synthesized (Scheme 97) <1998TL2103, 1999TL7219, 1999T13029>. 

The phosphonate 881 was also used in a Horner-Wittig reaction with di- and tricarbonyl compounds 883-885, containing thiophene spacer units, affording bis- and tris-(l,3-dithiole) donors 886 and 887, respectively (Scheme 133) <1995H(40)123, 1995CC557, 1997H(44)263>. 

Thin-layer chromatographic separation of a vinyl phosphate and a dithiolate and paper chromatography of phosphonates have been reported. 

In addition to acetal formation with simple alcohols, (oxoalkyl)phosphonic diesters afford dioxolanes or dithiolanes from 1,2-diols or 1,2-dithiols". It is possible to transpose 0X0 protecting groups as illustrated in equation 15 ( = 0,1 or 2 X, Y = O, S or NH)" ... 

Various types of condensation polymers such as aromatic polysulfonates and polysulfides, aromatic polyethers, aliphatic and aromatic polysulfides, and carbon-carbon chain polymers of high molecular weights by the phase-transfer catalyzed polycondensation fi-om combinations of aromatic disulfonyl chlorides, phosphonic dichlorides, activated aromatic dichlorides, and aliphatic dihalides, withbisphenol, aliphatic and aromatic dithiols, and active ethylene compounds. The two-phase polycondensation was generally carried out in a water-immiscible organic solvent-aqueous alkaline solution system at room temperature. The method of polycondensation offers a highly versatile and convenient synthetic method for a variety of condensation polymers. 

Phosphonates based on (1), i.e., (PI), can be prepared simply by heating 1,3-dithiole-2-thiones with a trialkyl phosphite at high dilution [215]. They react with aldehydes, ketones, 2-iminium-I,3-dithioles or dithiolium salts and selenium analogs to give larger molecules, precursors of extended tetrachalcogenaftil-valenes (see below). The reactions take place in the presence of a base, such as butyllithium (BuLi) or LDA. Some aldehydes and ketones, which have... 

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