Ethers, reaction with dithiols

The stoichiometric equivalents of halofluorides have been recently applied to transform alkylene dithioacetals into gcm-difluorides.70-71 Dithioacetals such as 1,3-dithiolanes and 1,3-dithianes arc readily obtained from the corresponding carbonyl compounds by the reaction with ethane-1,2-dithiol or propane-1,3-dithiol in the presence of the complexes boron trifluoride-bis(acetic acid) or boron trifluoride-diethyl ether. Using a two-step procedure, a range of aldehydes and ketones can be converted into gem-difluorides under mild conditions. 

Thioacetals. Aldehydes, ketones, or acetals, both cyclic and acyclic, can be converted into thioacetals by reaction with a thiol or dithiol and MgBr2 (2.1 equiv.) in ether at 25°. The difference in reactivity between acetals and ketones permits selective conversion of acetals into thioacetals without acetalization of a ketone. 

Recently it has been reported that a-thio derivatives of enamines and enol ethers form 5-amino- or 5-alkoxy-l,2-dithiole-3-thiones (127a, b) by reaction with carbon disulfide (80ZOR13). Spiran compounds (128) are also formed from suitable substrates. The reaction has some similarities to an enamine synthesis below <67AG(E)294). 

Base-mediated condensation reaction of 2,7-dibromotropone with dithiol afforded the 22-membered 79 and 44-membered products 80 in 62% and 24%, respectively (Scheme 11) <2004H(62)149>. Compound 79 was used as a carrier through a chloroform liquid membrane however, the guest selectivity of 79 was lower than that of the corresponding pentaoxadithiacrown ether 76. 

As seen in 10-6, departure of the leaving group from an acetal gives a particularly stable carbocation. It is also possible to convert a dimethylketal directly to a dithiane by reaction with butane 1,4-dithiol on clay. ° These are equilibrium reactions, and most often the equilibrium is shifted by removing the lower-boiling alcohol by distillation. Enol ethers can be prepared by treating an alcohol with an enol ester or a different enol ether, with mercuric acetate as a catalyst, example. 

Deaeetylation. Treatment of the acetylpyrrole 1 with BF3 etherate and ethane-dithiol in acetic acid gives the pyrrole 2 in quantitative yield. This reaction was first observed with the coppcr(ll) complex of the acetylporphyrin 3, which was converted to 4 in this way. The proposed mechanism involves protonation of the dithio-kctnl in situ. 

A variety of engineering polymers and copolymers can be prepared by reacting an aromatic ether dithiol (HS—C6H4OC6H4SH) which has just been stannylated [by reaction with bis(tri- -butyltin)oxide] with isophthaloyl chloride in dry chloroform. The polymer is precipitated from methanol and the infrared spectrum is consistent with the structure of the polymer [16a] as... 

Braun and Muijahn [75] reported that attempts to distill allyl mercaptan gave the pure product and a nondistillable residue. Braun and Plate [76] later reported that several other unsaturated mercaptans gave liquid polymers. Vaughan and Rust [77] obtained low-molecular-weight (less than 300) poly(alkylene sulfide) by the reaction of hydrogen sulfide and diallyl or diallyl ether. Coffinan [78] reported that polymeric alkylene sulfide of molecular weights to about 1300 were obtained by the reaction of dithiols with diolefins. 

Bradshaw and colleagues prepared numerous thiaox-acrown ethers by the reaction of polyethylene glycol dihalides with dithiols and sulfur-containing polyethers in ethanol with sodium or sodium hydroxide acting as the base." " The yields were quite variable and most compounds required chromatographic separation. 

Dithiols, like diols, have been protected as 5,5 -methylene, 5,5 -isopropylidene, and 5,5 -benzylidene derivatives, formed by reaction of the dithiol with formaldehyde, acetone, or benzaldehyde, respectively. The methylene and benzylidene derivatives are cleaved by reduction with sodium/ammonia. The isopropylidene and benzylidene derivatives are cleaved by mercury(II) chloride with sodium/ ammonia the isopropylidene derivative is converted to a monothio ether, HSCHR-CHRSCHMe2- ... 

A hydroxy and an arylthio group can be added to a double bond by treatment with an aryl disulfide and lead tetraacetate in the presence of trifluoroacetic acid." Manganese and copper acetates have been used instead of Pb(OAc)4. ° Addition of the groups OH and RSO has been achieved by treatment of alkenes with O2 and a thiol (RSH)." Two RS groups were added, to give vie- dithiols, by treatment of the alkene with a disulfide RSSR and Bp3-etherate."° This reaction has been carried... 

Dithioketals, especially the cyclic dithiolanes and dithianes, are also useful carbonyl-protecting groups. These can be formed from the corresponding dithiols by Lewis acid-catalyzed reactions. The catalysts that are used include BF3, Mg(03SCF3)2, Zn(03SCF3)2, and LaCl3.100 S-Trimethylsilyl ethers of thiols and dithiols also react with ketones to form dithioketals.101... 

Dithiolane-fused oxadithiepins, widely used in the synthesis of charge-transfer complexes, are available by [3+4] substitution reactions of dithiolane dithiolates with di(chloromethyl) ether (see Section 13.16.9.4.1). 

The reaction of aldehydes or ketones with ethane-1,2-dithiol or propane-1,3-dithiol to form 1,3-dithiolanes or 1,3-dithianes is an important reaction, as these compounds under suitable conditions are acyl anion equivalents (see Section 5.9, p. 626). These cyclic dithioacetals have been less used as protective groups, though when required are formed in high yield in the presence of boron trifluoride-etherate.138... 

Benzenedithiols are traditionally prepared by reductive dealkylation of 1,2-C6R4(SR )2, which in turn are obtained by treatment of dibromobenzenes with alkali metal or cuprous thiolates. The methodology continues to be used, for example, for crown ether-appended derivatives (15). A newer and more powerful synthesis of 1,2-benzenedithiol and its derivatives has been developed (16). This method (17) involves reaction of the benzenethiol with 2 equiv of BuLi to give 2-LiC6H4(SLi), which reacts with elemental sulfur to give the dithiolate (Eq. 1). 

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