Esters homoallylic

Si. rra(pentafluorophenyl)boron was found to be an efficient, air-stable, and water-tolerant Lewis-acid catalyst for the allylation reaction of allylsilanes with aldehydes.167 Sc(OTf)3-catalyzed allylations of hydrates of a-keto aldehydes, glyoxylates and activated aromatic aldehydes with allyltrimethylsilane in H2O-CH3CN were examined. a-Keto and a-ester homoallylic alcohols and aromatic homoallylic alcohols were obtained in good to excellent yields.168 Allylation reactions of carbonyl compounds such as aldehydes and reactive ketones using allyltrimethoxysilane in aqueous media proceeded smoothly in the presence of 5 mol% of a CdF2-terpyridine complex (Eq. 8.71).169... 

Allyllic ether 53 is oxidized regioselectively to the /3-alkoxy ketone 54, which is converted into the a,/i-unsaturated ketone 55 and used for annulation[99]. The ester of homoallylic alcohol 56 is oxidized mainlv to the 7-acetoxy ketone 57[99]. 

The carbopalladation is extended to homoallylic amines and sulfides[466. Treatment of 4-dimethylamino-l-butene (518) with diethyl malonate and Li2PdCl4 in THF at room temperature leads to the oily carbopalladated complex 519, hydrogenation of which affords diethyl 4-(dimethylamino) butylmalonate (520) in an overall yield of 91%. Similarly, isopropyl 3-butenyl sulfide (521) is carbopalladated with methyl cyclopentanonecarboxylate and Li2PdCl4. Reduction of the complex affords the alkylated keto ester 522 in 96% yield. Thus functionalization of alkenes is possible by this method. 

The acylpalladium complex formed from acyl halides undergoes intramolecular alkene insertion. 2,5-Hexadienoyl chloride (894) is converted into phenol in its attempted Rosenmund reduction[759]. The reaction is explained by the oxidative addition, intramolecular alkene insertion to generate 895, and / -elimination. Chloroformate will be a useful compound for the preparation of a, /3-unsaturated esters if its oxidative addition and alkene insertion are possible. An intramolecular version is known, namely homoallylic chloroformates are converted into a-methylene-7-butyrolactones in moderate yields[760]. As another example, the homoallylic chloroformamide 896 is converted into the q-methylene- -butyrolactams 897 and 898[761]. An intermolecular version of alkene insertion into acyl chlorides is known only with bridgehead acid chlorides. Adamantanecarbonyl chloride (899) reacts with acrylonitrile to give the unsaturated ketone 900[762],... 

The four-membered vinyloxetane 280 is cleaved with Pd(0j and used for allylation a homoallylic alcohol unit can be introduced into the keto ester 281 as a nucleophile with this reagent to form 282[168],... 

Base-induced elimination of sulphinate from homoallylic sulphones , from y-ketosulphones , and from 1,2-bissulphones has been used in synthetic sequences ranging from the preparation of retinoic acid and of its methyl ester , to a novel pentannulation sequence that leads to a range of cross-conjugated dienes , as exemplified by equation (69). The overall yield for the two steps was 63%. 

Table 5 summarizes the reactions of isoprene with aromatic aldehydes and unsaturated aldehydes. Salicylaldehyde provides the expected product as a cyclic boric ester derivative and shows apparently lower stereoselectivity, giving a mixture of 1,3-anti and 1,3-syn isomers in a ratio of 6 1 (run 1, Table 5). 2-Furfural reacts as usual and provides a 1,3-anti isomer as a single diastereomer in good yield (run 2). Unsaturated aldehydes, irrespective of their substitution patterns, undergo homoallylation selectively with excellent 1,3-anti selectivity, the geometry of the double bond of the starting aldehydes remaining intact (runs 3-5). 1,2-Addition to unsaturated aldehyde takes place selectively and no 1,4-addition is observed.

The application of RCM to dihydropyran synthesis includes a route to 2,2-disubstituted derivatives from a-hydroxycarboxylic acids. In a one-pot reaction, the hydroxy esters undergo sequential O-allylation, a Wittig rearrangement and a second O-allylation to form allyl homoallyl ethers 8. A single RCM then yields the 3,6-dihydro-2//-pyran 9. The process is readily adapted not only to variably substituted dihydropyrans but also to 2-dihydrofuranyl and 2-tetrahydrooxepinyl derivatives and to spirocycles e.g. 10 through a double RCM (Scheme 4) <00JCS(P1)2916>. 

Starting from 2,4,6-octatriene and pivaldehyde, the conjugated homoallylic alcohol 8 is obtained as the sole product. Cycloheptatriene-derived complexes react with aldehydes and C02 to afford mixtures of the isomeric 1,3- and 1,4-cycloheptadienyl carbinols or acids, respectively. Interestingly, analogous reactions with methyl chloroformate or dimethyl carbamoyl chloride produce the conjugated dienyl ester 9 or amide 10 as unique products [19,20]. 

The electrosynthesis of homoallyl alcohols (193) or 8-hydroxy esters (196) has been carried out by the reaction of methallyl chloride (190) (Scheme 75) or... 

Solutions of acetyl nitrate at subambient temperature can react with alkenes to yield a mixture of nitro and nitrate ester products. Cyclohexene forms a mixture of 2-nitrocyclohexanol nitrate, 2-nitrocyclohexanol acetate, 2-nitrocyclohexene and 3-nitrocyclohexene. This illustrates one of the problems of allylic and homoallylic alcohol 0-nitration with this reagent. 

Furthermore, the chloro ester 1-Me also readily reacted with the nitrile ylide 37 at room temperature, however, the pyrrole derivative 40 was the only isolated product (Scheme 9) [26 a]. The latter was obviously formed from the primary cycloadduct 38 by a cyclopropylcarbinyl to homoallyl rearrangement [1]. 

The addition of allylic boron reagents to carbonyl compounds first leads to homoallylic alcohol derivatives 36 or 37 that contain a covalent B-O bond (Eqs. 46 and 47). These adducts must be cleaved at the end of the reaction to isolate the free alcohol product from the reaction mixture. To cleave the covalent B-0 bond in these intermediates, a hydrolytic or oxidative work-up is required. For additions of allylic boranes, an oxidative work-up of the borinic ester intermediate 36 (R = alkyl) with basic hydrogen peroxide is preferred. For additions of allylic boronate derivatives, a simpler hydrolysis (acidic or basic) or triethanolamine exchange is generally performed as a means to cleave the borate intermediate 37 (Y = O-alkyl). The facility with which the borate ester is hydrolyzed depends primarily on the size of the substituents, but this operation is usually straightforward. For sensitive carbonyl substrates, the choice of allylic derivative, borane or boronate, may thus be dictated by the particular work-up conditions required. 

II-NMR analysis of derived pinanediol ester. b By 13C-NMR and GC analyses of derived 4-methyl-3-heptanol see text. c 1H-NMR analysis of derived symmetrical diol. The construction of R3 (Section 1.1.2.1.6.) was not totally stcrcospecific and may have been the source of the 12% diastercomeric contaminant. d From the ee of the homoallylic alcohol derivative formed by reaclion with benzaldchyde, measured by GC on a chiral column. 

We were particularly interested to see whether a regio- and stereoselective hy-droxyalkylation and amrnoalkylation of 1 and 2 with aldehydes and imino esters, perhaps by choice of the substituent X at the Ti atom, with formation of the corresponding sulfonimidoyl-substituted homoallyl alcohols 4-7 and the homoallyl amines 8-11 (Fig. 1.3.3) could be achieved. Reggelin et al. had already demonstrated that the sulfonimidoyl-substituted mono(allyl)titanium complexes 3, the... 

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