Carbinols divinyl

D,L-Arahinitol can be prepared by the action of hydrogen peroxide in the presence of formic acid on divinyl carbinol (36) and, together with ribitol (Fig. ld),fromD,L-erythron-4-pentyne-l,2,3-triol,HOCH2CHOHCHOHC=CH (37). 

Scheme 9.10 Vinylepoxide synthesis from divinyl carbinol.

The epoxidation of divinyl carbinol constitutes a special case of a dienol epoxida-tion, as the starting diene is not conjugated (Scheme 9.10). Desymmetrization by SAE, followed by a Payne rearrangement, furnishes the vinylepoxide in high yield and with excellent enantioselectivity (compare Table 9.2, Entry 1) [43]. 

Schreiber et al.47 have described a mathematical model that combines enantiotopic group and diastereotopic face selectivity. They applied the model to a class of examples of epoxidation using several divinyl carbinols as substrates to predict the asymmetric formation of products with enhanced ee (Scheme 4-28). 

Scheme 4-28. The asymmetric epoxidation of divinyl carbinols. Reprinted with permission by Am. Chem. Soc., Ref. 47b. 

Three divinyl carbinol substrates have been chosen as examples. They are good substrates for examination because the vinyl carbinols are known to undergo Sharpless reaction at low reaction rates. The results presented in Table 4-7 clearly show that the ee of 79 improves as the reaction proceeds toward completion. Note that the minor enantiomer 78 can be removed through a second, faster epoxidation that converts enantiomer 78 into an easily destroyed bis-epoxide 80 (Scheme 4-29 and Table 4-7). The same trend is apparent in the second demonstration with diisopropenyl carbinol 81 (Scheme 4-30 and Table 4-8). Similarly, the third reaction is the reaction of (E,E)-divinyl carbinol 82 (Scheme 4-31 and Table 4-9). 

Triflates also undergo Heck reactions and Gribble and Conway reported several such couplings of l-(phenylsulfonyl)indol-3-yl triflate (34) to afford 3-vinylindoles 224 [183]. Cyclohexene, allyl bromide, and methyl propiolate failed to react under these conditions, but triphenylphosphine afforded 225 in excellent yield (93%), and divinyl carbinol yielded the rearranged enal 226 (82% yield). 

Methylenebis(oxy) ]bis(2-chloroformaldehyde), see Bis (2-chloroethoxy) methane Methylene chlorobromide, see Bromochloromethane Methylene dichloride, see Methylene chloride Methylene dimethyl ether, see Methylal Methyl 2,2-divinyl ketone, see Mesityl oxide Methylene glycol, see Formaldehyde Methylene glycol dimethyl ether, see Methylal Methylene oxide, see Formaldehyde Methyl ethanoate, see Methyl acetate (1 -Methylethenyl)benzene, see a-Methylstyrene Methyl ethoxol, see Methyl cellosolve 1-Methylethylamine, see Isopropylamine (l-Methylethyl)benzene, see Isopropylbenzene Methylethyl carbinol, see sec-Bntyl alcohol Methyl ethylene oxide, see Propylene oxide ds-Methylethyl ethylene, see cis-2-Pentene frans-Methylethyl ethylene, see frans-2-Pentene Methyl ethyl ketone, see 2-Bntanone Methylethylmethane, see Butane... 

The addition of aryl halides and divinyl or enyne carbinols to give tri- or tetra-substituted alkenes is considered to involve skeletal reorganization (Scheme 89) of an intermediate cyclopropanol.132 The ability to suppress /3-hydride elimination of organopalladium intermediates is critical to the success of these processes. 

Smith, D S, Wang, Z, Schreiber, S L, The asymmetric epoxydation of divinyl carbinols theory and applications. Tetrahedron, 46, 4793-4808, 1990. 

Another new synthesis of 77-allyl complexes is the reaction of divinyl carbinols with palladium(II) salts in methanol or ethylene glycols 270). In methanol, either 1,5- or 1,2-addition of methoxide occurred, whereas ethylene glycol gave a dioxanyl 77-allylic palladium complex. 

The work of Martin and co-workers [49] has shown that excellent diastereo-control can be achieved in cyclopropanation of single enantiomers of chiral secondary diazoesters by catalyst matching. Thus, while Rh2(5R-MEPY)4 and the (S)-diazoester in Eq. (27) react to afford a 37 63, endo exo mixture of diastereoi-someric cyclopropanes, the 5S-MEPY catalyst affords a >95 <5 ratio of the same products. A final illustrative example of the versatility of this methodology is shown in Eq. (28). Here diazoacetates of prochiral divinyl carbinols undergo intramolecular cyclopropanation catalysed by Rh2(5S-MEPY)4 with exceptional enantiocontrol [49]. 

Group selective reactions of divinyl carbinols. It is important to remember that the reagent control strategy is inapplicable to situations where the resident chirality is on the allylic position bearing the hydroxyl handle for the catalyst. However, the pref-... 

Scheme 8.10. Reaction of divinyl carbinol under (+)-AE conditions as an example of enantiotopic group selectivity in epoxidation chemistry. Matched cases of enantiofacial selectivity are shown with bold arrows. Qualitative rate differences are on the order kj k2, ks k4 (without specifying an order for k2 vi. k3 (however, cf. Scheme 8.8b). Note that the products arising from the pairs ki/k3 and k2/k4 are enantiomers.

In recent years the discovery of novel methods of asymmetric synthesis has greatly increased the ability of organic chemists to synthesize optically active sugars. For example, the asymmetric epoxidation reaction discovered by Katsuki and Sharpless [142] was recently used as the key step in a synthesis of D-oleandrose 118 from divinyl carbinol 119 by Hatakeyama et al. [143]. An alternative approach to asymmetric synthesis of oleandrose was taken by Danishefsky et al. [144,32] in their synthesis of avermectin which is the first, and currently the only, reported total synthesis of an avermectin. The key step of this synthesis was a cyclocondensation reaction of optically active diene 121 with acetaldehyde catalyzed by the optically active Lewis acid (-h)-Eu(hfc)3 [145]. The resulting chiral pyrone was then elaborated to methyl-L-oleandroside 113. This was further converted to the disaccharide glycal 122 by a 4 step sequence in which glycoside formation was accomplished by iV-iodosuccinimide mediated addition of the alcohol to a glycal followed by tributyltin hydride... 

Tartrate esters also feature as the chiral reagents in the Sharpless asymmetric epoxidation, a reaction applied in the synthesis of deoxy-sugars. Two groups have epoxidized divinyl carbinol (33) and converted the resulting mono-epoxlde (3 ) into the 2,6-dideoxy-sugars D-ollvose (35), its 3- -niethyl ether (D-oleandrose) and 4-0 -benzyl ether, and Into D-digltoxose (36) and Its 4- -benzyl ethers (Scheme 7). Epoxidation of the meso-... 

The addition of an Si-H bond across a C-C double bond is called hydrosilylation, and this reaction is presented in Chapter 16. The alkylsilane products of hydrosilylation can be converted to alcohols upon oxidation of the newly formed Si-C bond. Thus, desymmetrization of divinyl carbinols by hydrosilylation can generate enantioenriched 1,3-diols. In the presence of a (R,R)-DIOP-based rhodium catalyst, intramolecular hydrosilylation of a 3,5-dimethylphenyl-substituted silane derivative formed the cyclic product in Figure 14.34 in 93% ee. ... 

When divinyl carbinols are heated with dimethylacetamide dimethyl acetal (4), the less substituted and less electron-rich double bond engages in the rearrangement (Scheme 7.13, Eqs. 1 and 2) [29]. Vinyl-propargyl carbinols were found to rearrange with preferential participation of the double bond (Eq. 3) [30]. For another case of a highly regjoselective Eschenmoser-Qaisen rearrangement see Scheme 7.16, Eq.4[31]. 

A monograph (in Russian) has appeared on catalytic hydrogenation and hydro-genolysis of carbohydrates. The influence of the composition of nickel-alumina and other catalysts on the hydrogenolysis of D-glucose has been investigated. DL-Arabinitol, ribitol, and xylitol have been synthesized from 3-hydroxypenta-1,4-diene (divinyl carbinol) by the routes outlined in Scheme 80. ... 

Before dedicating efforts to the synthesis of the specific system required, a model system was again utilized (Scheme 7). As such, butyiyl chloride was reacted with divinyl carbinol, the resulting ester (45) was deprotonated and... 

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