Unsaturated -hydroxy

The cyclization of the homologous epoxide 36 under acidic conditions was also investigated (Table 9.5) [110]. As would be expected, compound 36a reacted by a 6-exo cyclization to give tetrahydropyran 38a (Entry 1). The a, 3-unsaturated hydroxy epoxide 36b gave a 1 3.5 mixture of oxepane 37b and tetrahydropyran 38b (Entry 2). Subjection of 36c and 36d, which both contain more electron-rich 71-systems, to the reaction conditions resulted in preferential 7-endo cyclization to give 37c and 37d, thus confirming the powerful regiodirecting effect of the vinyl moiety (Entries 3 and 4). 

It is also possible to oxidize allenes 89 and 92 to unsaturated hydroxy ketones 91 and 93 via the spirodioxide intermediate 90 [29]. In this case the terminating step is a 1,5-proton shift. In the examples shown in Scheme 17.26, the formation of the spirodioxide intermediate is diastereoselective, as is the rearrangement to the unsaturated hydroxy ketone. 

Reformatsky reaction.5 The Reformatsky reaction of y-bromocrotonic acid with aldehydes or ketones in THF gives rise to a mixture of branched and linear unsaturated hydroxy acids. The former are the kinetic products and, on equilibration, rearrange to the latter products. 

Several recent reviews have included specific types of electrophilic cyclofunctionalization reactions.1 Important areas covered in these reviews are halolactonization u cyclofunctionalization of unsaturated hydroxy compounds to form tetrahydrofurans and tetrahydropyrans lb cyclofunctionalization of unsaturated amino compounds lc cyclofunctionalization of unsaturated sulfur and phosphorus compounds ld lf electrophilic heterocyclization of unconjugated dienes 1 synthesis of y-butyrolactones 1 h synthesis of functionalized dihydro- and tetrahydro-furans lj cyclofunctionalization using selenium reagents lk lm stereocontrol in synthesis of acyclic systems 1" stereoselectivity in cyclofunctionalizations lP and cyclofunctionalizations in the synthesis of a-methylenelactones.lq Previous reference works have also addressed this topic.2... 

A detailed study of the iodocyclization of a series of unsaturated hydroxy acids has demonstrated that a ground-state conformational analysis can serve as a reliable indicator of the relative reactivities of various conformations. Thus, while 153 undergoes exclusive iodolactonisation, 154 gives the corresponding iodotetrahydrofuran as the sole product, in full agreement with the MM2 prediction224. 

Enantioselective isomerization can be advantageously used for the kinetic resolution of racemic allyl alcohols. For example treatment of 4-hydroxy-2-cyclopente-none (rac-28) in the presence of Rh[(R)-BINAP](MeOH)2 + gives rise to the enan-tiomerically enriched allyl alcohol (R)-29 (Scheme9) [13]. This unsaturated hydroxy ketone is an important building block for the synthesis of prostaglandins... 

Hydroxydec-2-enoic acid 397 was identified in the fodder juice of the Weisel cells (gelee royale) of honey bees. One of the synthesis of 397 starts from suberic acid ethylester 393 222) which was first converted into the hydroxyacid 394 and then into the thiol ester 395. Raney nickel reduction of the latter yields an intermediate aldehyde which, in statu nascendi, reacts with the phosphorane 67 to give 396. Subsequent hydrolysis of396affords the ( )-a,0-unsaturated hydroxy acid 397 222) (Scheme 70). 

The prostaglandins are C20 unsaturated hydroxy acids with a substituted cyclopentane ring and two aliphatic side chains. 

Kato, T., Yamaguchi, Y., Hirano, T., Yokoyama, T., Uyehara, T., Namai, T., Yamanaka, S., and Harada,N. 1984. Unsaturated Hydroxy Fatty-Acids, the Self Defensive Substances in Rice Plant against Rice Blast Disease. Chem. Lett., 409-412. 

Unsaturated hydroxy fatty acids, the self-defensive substances in rice plant against Rice Blast Disease. Chem. Lett., 25, 409 112. 

Table 18 Diels-Alder Reactions of a,p-Unsaturated Hydroxy Ketones with Cyclopentadiene (Scheme 83)...

Triphenyl phosphite ozonide, (CtHsOjjPOj, which is obtained by ozonization of triphenyl phosphite in dichloromethane solution at -78 °C, decomposes to triphenyl phosphate and singlet oxygen [178]. As an oxidant, it converts the trimethylsilyl ethers of enols of a,p-unsaturated ketones into unsaturated hydroxy ketones [996]. 

These are a,P.Y 5-unsaturated carbonyl compounds, known to undergo Michael type addition. As a consequence they readily add water, resulting in generation of unsaturated hydroxy-oxo acids (Scheme 8). 

The reactim of 2-cyclohexenone with 2-lithiodithiane occurs in a 1,2-fashion to give the unsaturated hydroxy derivative, which, after rearrangement followed by deprotection, gives 3-hydroxy-1-cyclohex-enecarbaldehyde. ... 

Tetrahydrofurans, synthesis via intramolecular cyclization of unsaturated hydroxy compounds 82KGS1443. 

One step in the production of (5), a key intermediate in a synthesis of the tetracyclic triterpene a-onocerin, involved allylic oxidation of the a,)3-unsaturated ester (1). This was accomplished with Se02 in boiling acetic acid.18b The unsaturated hydroxy lactone produced (2) was next to be converted into the saturated keto acid (5), presumably by a stepwise process. However, the Israeli investigators were pleas-... 

Benzyl, allyl, vinyl, and aryl, but also some aliphatic, halides have been transformed into carboxylic acids (Eq. 10). Under other conditions, couplings with CO to give symmetrical or unsymmetrical ketones were possible. Epoxides yielded unsaturated hydroxy acids, and a-oxo-butyrolactones (Eq. 11), couplings of alkynes and alkyl halides gave hydroxybutenolides (Eq. 12) and other more complex conversions could also be realized. 

Klenk and Schorsch72 have elaborated an excellent method for the separation of the individual, genuine galactocerebrosides. The crude cerebroside fraction obtained by solvent extraction of a suitable tissue is separated by chromatography on silica gel. Cerebrosides containing saturated or unsaturated hydroxy fatty acids can be separated from those containing nonhydroxy fatty acids. In both of the separated parts, there are numerous individual cerebrosides. 

Trost has used a,a-disulfenylated lactones as enolate precursors. As shown in equation (23), a,a-di-(phenylthio)- v-butyrolactone is treated sequentially with ethylmagnesium bromide and acetaldehyde to obtain -hydroxy lactone (8) in virtually quantitative yield. Oxidation of the phenylthio group and subsequent elimination of the resulting sulfoxide provides the unsaturated hydroxy lactone (9). The process was employed with more complex lactones in a total synthesis of iridoids. The method fails with a,a-di-sulfenylated ketones unless a catalytic amount of copper(I) bromide is included in the reaction mixture. 

Considering this information, another method was worked out as described in Chart 14. The lactone ring of compound (51) was cleaved by potassium hydroxide and careful neutralization gave the unsaturated hydroxy acid (54). Crude compound (54) was hydrogenated on Pd-C in EtOH and the reaction mixture was subsequently acidified with concentrated hydrochloric acid. After usual worked-up, the reaction mixture showed the existence of two products on thin layer chromatography. 

A similar structure was seen in Aspergillus oryzae, the Japanese yellow mold (75). Trans-unsaturated hydroxy fatty acids ( 2-hydroxyoctadec-3-enoic acid) found in F. amygdali and A. oryzae cerebrosides have not been detected in sphingolipids of animals and plants. 

Acyl anion equivalents. Addition of the title reagents to enones occurs in the 1,2-mode. This Pd-catalyzed reaction provides unsaturated hydroxy ketones. 

Unsaturated hydroxy carboxylates of the type (7 )-R-CH=CH-CHOH-COO which were prepared from the corresponding 2-oxo carboxylates could be converted to various products with additional chiral centres with reasonable or excellent diastereoselectivity (Table 13) (44,45). A series of kinetic data for reductions and dehydrogenations are shown in Table 9. The mechanism of HVOR is not known yet. It seems not to be a ping pong mechanism since the values of 2-oxo carboxylates depend on the applied mediator. The temperature dependence of HVOR with reduced methylviologen and 3-phenylpyruvate shows an increase from 24-39 °C of about 2 fold per 10 °C (48). 

Reaction with allylic and homoallylic hydroxysteroids. Westphal and Zbiral have reported the reaction of lead tetrakis(trifluoroacetate) with a number of unsaturated hydroxy steroids. 

---