Allyl transfer reaction

This allyl transfer reaction, which is a valuable synthetic method, has been shown to be a free-radical chain substitution (SH2 ), namely... 

The allylic HYCRAM derivative was subsequently modified by insertion of a standard amino acid between the aminomethyl resin and the hydroxy butenoic acid moiety. Using this allylic anchor, the resin-linked, glycosylated HIV peptide T-derivative 164 was synthesized by application of Fmoc amino protection and sidechain protection with lert-butyl groups. The lac-tosamine peptide T (165) could be released from the resin by application of the palladium(0)-catalyzed allyl-transfer reaction to V-methyl aniline as the allyl acceptor. 

Diethylamine (11) is an inexpensive base that removes fluorenylmethyl-based protectors without forming an adduct with the liberated moiety, and it can be eliminated by evaporation. It has been employed as nucleophile for palladium-catalyzed allyl-transfer reactions (see Section 3.13). 

The allyl-transfer reaction based on 2-oxonia Cope rearrangement allows highly stereocontrolled chirality transfer. Triflic acid has been shown to induce the rearrangement of the 251 allyl sterols into 22-homoallylic sterols with high stereoselectivity without side reactions86 [Eq. (5.316)]. The protocol, however, is not effective for syn substrates (for example, 251, R = H, R = COOEt). 

Scheme 9.29. Enantioselective three-component free-radical addition—allyl-transfer reaction.

Nokami, J. Ohga, M. Nakamoto, H. Matsu-bara, T. Hussain, I. Kataoka, K. The first and highly enantioselective crotylation of aldehydes via an allyl-transfer reaction from a chiral crotyl donor. /. Am. Chem. Soc. 2001, 123, 9168-9169. 

Nokami, J. Nomiyama, K. Matsuda, S. Imai, N. Kataoka, K. Highly enantioselective alk-2-enylation of aldehydes through an allyl-transfer reaction. Angew. Chem. Int. Ed. 2003, 42, 1273-1276. 

Enholm [12] has carried out free radical allyl transfer reactions using a non-cross-linked polystyrene, soluble polymer 77. Model reactions of bro-mo ester 78 with allyltin reagents gave products 79 and 80 in excellent yield (Scheme 17). 

The reaction products were isolated as stable phosphine derivatives. In the reaction with l,l,2-trimethyl-7r-allylpalladium chloride Heck isolated a compound whose structure probably resembles that of the intermediate in other allyl transfer reactions 159) ... 

It has been found that under similar, and even more drastic conditions, the nickel complexes do not react with metallic mercury. Formally the reaction of allylpalladium complexes with metallic mercury might be regarded as a redox process. However, since metals which behave as stronger reducing agents than mercury do not enter the 7r-allyl transfer reaction this argues against a simple redox mechanism for 7r-allyl transfer from palladium to mercury. 

Oxazolidinones used in conjunction with Lewis acids promote radical atom transfer sequences with inactivated alkenes, and these reactions proceed with good to excellent selectivity [32]. In the absence of Lewis acid, poor conversion was seen. Several common Lewis acids (e.g. MgBr2, Zn(OTf)2, and La(OTf)3), which are effective promoters of the allyl transfer reaction described in Eq. (22), failed to improve conversion significantly. Sc(OTf)3 performed moderately well with the 1° bromide while Yb(OTf)3 gave excellent yields of product. With terminal alkenes, the reactions were rapid and efficient complete conversion was seen within 15 min at room temperature. Internal alkenes were slower to react, but near quantitative yields were possible with cis alkenes in reactions promoted by Yb(OTf)3. 1,2-Di-chloroethane (DCE) appears to be a particularly good solvent for these transformations. 

High threo selectivity in allyl transfer reactions giving n = 2 telomers has been observed using achiral oxazolidone acrylamides (Fig. 7). Selectivities as high as 93 7 in favor of threo products were obtained in pentane. Selectivity also appeared to depend on solvent polarity with higher selectivities in solvents of lesser polarity [7]. The n = 2 telomers from the allyl transfer reaction of cyclododecyl iodide and allyl stannane can be crystallized, and the X-ray crystal structure of the threo product... 

Longifolene [( + )-47] is a natural product from Indian terpentine oil and is commercially available so that chemical synthesis is unnecessary. On hydroboration with borane-dimethyl sulfide complex, diisolongifolylborane (48) is formed, a stable, isolable compound (for a detailed description, see ref 36). It has been utilized as achiral reagent in allyl transfer reactions (Section D.2.5.2.). 

Sumida S, Ohga M, Mitani J, Nokami J (2(X)0) New and Stereoselective Synthesis of 1,4-Disubstituted Buten -ols (Homoallylic Alcohol a-Adducts) from the Corresponding y-Isomers (3,4-Disubstimted Buten-4-ols) via an Acid-catalyzed Allyl-Transfer Reaction with Aldehydes. J Am Chem Soc 122 1310... 

Nokami J, Ohga M, Nakamoto H, Matsubara T, Hussain I, Kataoka K (2001) The First and Highly Enantioselective Crotylation of Aldehydes via an Allyl-transfer Reaction from a Chiral Crotyl-donor. J Am Chem Soc 123 9168... 

Nokami J, Nomiyama K, Shafi SM, Kataoka K (2004) A Novel Enantioselective (2Z)-AIk-2-enylation of Aldehydes via an Allyl-Transfer Reaction from Chiral Allyl Donors Prepared from (-l-)-Isomenthone. Org Lett 6 1261... 

Yu C-M, Youn J, Jung H-K (2006) Regulation of stereoselectivity and reactivity in the inter-and intramolecular allylic transfer reactions. Bull Korean Chem Soc 27 463-472... 

The mild and selective nature of the palladium-catalysed allylation reaction has made it suitable for protection. Allyl ethers, esters, amines and carbamates can usually be easily formed by standard procedures. The allyl group can be removed later by exposme to a palladium catalyst and a competitive nucleophile, Y (Scheme 9.68). This is an allyl transfer reaction. Commonly used competitive nucleophiles for allyl esters of carboxylic acids include sodium 2-methylhexanoate, secondary amines such as pyrrolidine (Scheme 9.69) and morpholine, and dimedone. ... 

Allylboronates have gained a prominent position as a useful class of synthetic intermediates in the past 25 years. Figure 6.1 shows the general structure of allylboronates (1). The main use of these reagents is in the stereoselective synthesis of homoallylic secondary alcohols by an allyl transfer reaction to aldehydes (Section 6.3.1) [1-6). 

A gaUium-mediated allyl transfer reaction proceeds in a stereospecific manner (Scheme 1.49) [63g]. An eryt/zro-tert-homoallyl alcoholate reacted with benzalde-hyde to afford an eryt/zro-sec-homoallyl alcohol. On the other hand, the reaction of a f/zreo-tert-homoallyl alcoholate provided a fereo-sec-homoallyl alcohol. A six-membered transition state with the bulky mesityl substituent at the equatorial position was assumed for the stereospecificity. 

A combination of palladium acetate and tricyclohexylphosphine is an effective catalyst. The allyl transfer reactions proceed in the presence of the catalyst and cesium carbonate in refluxing toluene. Homoallylic alcohol 1 transfers the methallyl group to a variety of aryl halides (Scheme 5.9) [12b]. The reactions under microwave irradiation at 250 "C go to completion in 15 min [12c]. The catalyst loading can be reduced to 0.05 mol% in the reaction of ethyl chlorobenzoate under microwave heating. 

Ever since the discovery that allylboranes could add in a nucleophilic fashion to aldehydes and ketones in 1964,carbonyl allylboration reactions have been thoroughly utilized in organic chemistry. Modification of allylic boron reagents and the substrates with which they can react has been the focus of many research groups over the past three decades. The application of allylbor-onates in the context of aldehyde allylation, which results in the formation of homoaUylic secondary alcohols via an allyl transfer reaction with aldehydes, has become an invaluable tool to synthetic chemists (Figure 3). ... 

The first reports of radical addition-fragmentation processes appeared in the synthetic organic chemistry literature in the early 1970s. Well-known examples of processes that involve a reaction step with an Sh2 mechanism include allyl transfer reactions with allyl sulfides and stannanes (the Keck... 

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