Epoxy sulfides

The reactivity of epoxides can be modified by various proximal functionality. For example, 2,3-epoxy sulfides 118 are converted to the corresponding TMS-thiiranium species 119 upon treatment with TMS triflate. This intermediate reacts with O-silyl amides regiospecifically to form l-substituted-3-hydroxy-2-thioethers (e.g., 120). Simple primary amines undergo polyalkylation, but imines can be used as an indirect amine equivalent <96TET3609>. 

Asymmetric oxidation of 2,3-epoxy sulfides (70) with (—)-(69), double stereodifferentation, gave... 

Payne reaction. Recent methodology takes advantage of the same anchimeric activity in optically active 2,3-epoxy sulfides and 2,3-epoxy amines (82 and 85), whereby treatment with Lewis acid induces rearrangement to the corresponding thiiranium and aziridinium ions (83 and 86) as reactive intermediates which react efficiently with a variety of nitrogen-based nucleophiles to give functionalized hydroxy sulfides (84) or hydroxy amines (87) <97SL11>. 

Scheme 10.6 Thia-Payne rearrangement nf representative 2..3-epoxy sulfides.

Asymmetric oxidation of 2,3-epoxy sulfides with (—)-(l), double stereodifferentiation, gives 2,3-epoxy sulfoxide diastereoiso-mers (eq 3). Lower de values were observed for the other epoxy sulfide enantiomer. The modified Sharpless reagent gave better de values (5.1 1) with the methyl sulfides. 

The scope of regio- and stereo-selective synthesis of vinylallenes by 1,5-(>S )-substitution of enyne acetates and oxiranes with organocuprates has been explored the products are usually obtained as mixtures of E- and Z-isomers (Scheme 12), ° Optimum conditions for stereoselective alkynylation of trans-2,3-epoxy sulfides at C(2), with double inversion of configuration, on reaction with alkynylaluminiums (Scheme 13) have been sought. 

The ring-opening reaction of epoxy sulfides with phenylboronic acid in boiling benzene presumably occurs stereoselectively (de>99%) via episulfonium ions, as shown in Scheme 67 and Table 9 <1999TL3191>. 

Table 9 Reaction of epoxy sulfides with phenylboronic acid...

In an attempt to further extend the foregoing methodology to include the preparation of o,p-epoxy sulfides, the condensation of chloromethyl p-tolyl sulfide and benzaldehyde using a protocol similar to that employed successfully in the sulfone case (Bu OK) gave only poor conversion to the desired epoxide. However, addition of the hindered amine base 1,4-diazabicyclo[2.2.2]octane (DABCO) results in the formation of the isomeric expoxides (29) in good yield (equation 9). In the case of benzaldehyde, the cis-epoxide predominates over the trans-epoxide (29b 82% versus 18%), while in the corresponding condensation with pivalaldehyde, the only epoxy sulfide obtained is the cis isomer (29c). Several attempts to effect an analogous reaction with ketones were unsuccessful formation of (30) (displacement-elimination) becomes the favored process (equation 10). 

A low yield of 8-hydroxy-a-chloro sulfide is obtained from the reaction of / tolylthiochloromethyllithium with benzaldehyde, presumably due to the inefficient generation of the carbanion with n-butyllithium. The phenylthio analog of the a,/8-epoxy sulfide... 

Under favorable conditions, the hydroxyl group of boronic acids can serve as a nucleophile. For example, epoxy-sulfides are opened stereoselectively by phenylboronic add to afford diol products (Equation 88, Figure 1.41) [465]. A new variant of this process makes use of a palladium catalyst [466]. Boronic acids have been employed recently as internal nudeophiles in a bromo-boronolactonization of olefins (Equation 89) [467]. 

The epoxy sulfides 110 and the corresponding amines 111 obtained this way, if treated with TMSOTf as the Lewis acid, undergo what one may call a hetero-Payne reaction at —78° aheady. As the cyclic onium cations are of course excellent electrophiles they also undergo ring opening at this low temperature. 

Scheme 3 Opening of rraw-epoxy sulfides 2 using AlMe3...

Conversely, the opening of fra/is-epoxy sulfides 2 using Mc3Al results in the substitution occurring at the C2 position to provide the corresponding products 3 with retention of the configuration (Scheme 3) [15, 16]. The possible reaction intermediate is a/iri-episulfonium ion, and overall double inversion of the stereochemistry is observed. In a related report, it was revealed that a reaction of epoxy selenides proceeds with the similar stereochemical outcome via an episelenmiium ion intermediate [17]. 

Sasaki M, Tanino K, Miyashita M (2001) Stereospecific alkyl and alkynyl substitutimi reactions of epoxy sulfides with organoaluminums with double inversion of the configuration. J Org Chem 66 5388-5394... 

The reaction of epoxy sulfides 1 and 2 with organoaluminium reagents is both re-gioselective and stereospecific. Thus, treatment of cw-l-(phenylthio)-2,3-epoxyalkanes 1 with excess of MesAl yielded after aeid quenehing, ri-hydroxy sulfides 3, whereas raK5-l-(phenylthio)-2,3-epoxyalkanes 2 under the same conditions, yielded 5y -hydroxy sulfides 4. In both cases the yields of isolated products were greater than 95% (Scheme 6.1). 

In addition to carbon and glass fibers ia composites, aramid and polyimide fibers are also used ia conjunction with epoxy resias. Safety requirements by the U.S. Federal Aeronautics Administration (FAA) have led to the development of flame- and heat-resistant seals and stmctural components ia civiUan aircraft cabias. Wool blend fabrics containing aramids, poly(phenylene sulfide), EDF, and other inherently flame-resistant fibers and fabrics containing only these highly heat- and flame-resistant fibers are the types most frequently used ia these appHcations. 

Other modifications of the polyamines include limited addition of alkylene oxide to yield the corresponding hydroxyalkyl derivatives (225) and cyanoethylation of DETA or TETA, usuaHy by reaction with acrylonitrile [107-13-1/, to give derivatives providing longer pot Hfe and better wetting of glass (226). Also included are ketimines, made by the reaction of EDA with acetone for example. These derivatives can also be hydrogenated, as in the case of the equimolar adducts of DETA and methyl isobutyl ketone [108-10-1] or methyl isoamyl ketone [110-12-3] (221 or used as is to provide moisture cure performance. Mannich bases prepared from a phenol, formaldehyde and a polyamine are also used, such as the hardener prepared from cresol, DETA, and formaldehyde (228). Other modifications of polyamines for use as epoxy hardeners include reaction with aldehydes (229), epoxidized fatty nitriles (230), aromatic monoisocyanates (231), or propylene sulfide [1072-43-1] (232). 

Sharpless and Masumune have applied the AE reaction on chiral allylic alcohols to prepare all 8 of the L-hexoses. ° AE reaction on allylic alcohol 52 provides the epoxy alcohol 53 in 92% yield and in >95% ee. Base catalyze Payne rearrangement followed by ring opening with phenyl thiolate provides diol 54. Protection of the diol is followed by oxidation of the sulfide to the sulfoxide via m-CPBA, Pummerer rearrangement to give the gm-acetoxy sulfide intermediate and finally reduction using Dibal to yield the desired aldehyde 56. Homer-Emmons olefination followed by reduction sets up the second substrate for the AE reaction. The AE reaction on optically active 57 is reagent... 

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