Protocol Yamamoto

With a twist on the Sharpless asymmetric epoxidation protocol, Yamamoto and co-workers <99JOC338> have developed a chiral hydroxamic acid (17) derived from binaphthol, which serves as a coordinative chiral auxiliary when combined with VO(acac)j or VO(i-PrO)j in the epoxidation of allylic alcohols. In this protocol, triphenylmethyl hydroperoxide (TiOOH) provides markedly increased enantiomeric excess, compared to the more traditional t-butyl hydroperoxide. Thus, the epoxidation of E-2,3-diphenyl-2-propenol (18) with 7.5 mol% VO(i-PiO)3 and 15 mol% of 17 in toluene (-20 °C 24 h) provided the 2S,3S epoxide 19 in 83% ee. 

Prior to the usage of the Ti-based catalytic system , the Sharpless group had reported their first asymmetric epoxidation of allylic alcohols using a combination of VO(acac)2/ TBHP and the chiral hydroxamic acid 67 (ee < 50%) or derivatives (ee 80%) ". In 1999, Yamamoto and coworkers described an improvement of this oxidation protocol, ee values up to 94%, by using hydroxamic acids derived from binaphthol, 68 being the... 

Polystyrene-bound pyridineboronic acid 5 is another example of an acylation catalyst which is easily recovered and reusable. Based on work by Yamamoto and coworkers [10] Wang et al. [11] developed an acylation protocol for amines, in which the carboxylic acid is... 

Z E = 49 1). At this stage, the (Z)-diene unit was introduced utilizing the Yamamoto olefmation protocol to give 43 [115]. A further five steps were then required to complete Smith s first-generation synthesis of (-)-discodermolide (ent-1), in 2.2% overall yield over 28 steps in the longest linear sequence based on the C1-C8 aldehyde 28. 

Discoveries made in the late 1970s of electrical conductivity in conjugated polymers spawned a monumental interest in the study of these materials, which are ideally suited for synthesis via cross-coupling reactions. Yamamoto was the first to realize this possibility with a regiochemicahy defined synthesis of poly(/ -phenylene) formed via the Kumada-Corriu protocol. Since then, various cross-coupling reactions have been applied in condensation polymerization reactions,with the Suzuki and Sonogashira protocols gaining the most widespread use. 

Recently, a yn-bicyclopropyl derivative 112 as a single isomer with > 90 /o de has been prepared by following the Yamamoto protocol for asymmetric cyclopropanation. ... 

Y. Komada, E. Azuma, H. Yamamoto, et al. Discontinuing therapy in childhood acute lymphoblastic leukemia treated with a chemoimmunotherapy protocol. Cancer Immunol. Immunother. 29 51 (1989). 

All partially bridged PPPs have been synthesized by the Yamamoto-type homocoupling protocol using preformed building blocks (e.g., dialkylfluorene, tetraalkylmdenofluorene, and octasubstituted penta-phenyl blocks). The fuUy bridged ladder polymer MeLPPP has been synthesized by the already outlined cyclization protocol of suitably substituted, single-stranded PPP precursors (Scheme 5.2). 

Another interesting methodological approach represents the use of NMR data to characterize and optimize the production of bicelles to study protein structure in lipid environments without the need for isotopic enrichment for solution NMR and to follow lipid-peptide interactions, as described by Al-Soufi et al and Yamamoto et al As an example, Morrison and Henzler-Wildman described a reconstitution protocol for the small multidrug resistance transporter, EmrE, which is highly sensitive to its environment, into isotropic bicelles with improved sample stability and expanded lipid composition profile. Furthermore, Lyukmanova et u/. characterized lipid-protein nanodiscs for cell-free production of integral membrane proteins in a soluble and folded state and compared their properties with detergent micelles, bicelles and liposomes. 

Hagiwara H, Kobayashi K, Miya S, Hoshi T, Suzuki T, Ando M, Okamoto T, Kobayashi M, Yamamoto I, Ohtsubo S, Kato M, Uda H (2002) First Total Syntheses of the Phytotoxins Solanapyrones D and E via the Domino Michael Protocol. J Org Chem 67 5969... 

Yamamoto has since shown this same reaction protocol can provide multicomponent access to tetrazoles, via the replacement of alkyne cycloaddition with that of substituted nitriles (Scheme 6.68) [95], This transformation proceeds with good product diversity. More recently, Barluenga has developed a bimolecular version for this reaction employing vinylbromides and sodium azide, providing access to N-unsubstituted triazoles [96]. 

A major limitation of Yamamoto s and the early de Meijere s protocols is the employment of EWG-activated alkynes to achieve synthetically useful yields of pyrrole products. A recent work from de Meijere s group revealed that this issue can be resolved by employing stoichiometric amounts of a slightly modified Cu(I) system. Accordingly, terminal alkynes 326 were shown to undergo the Cu(I)-mediated formal [3 + 2] cycloaddition reaction with isocyanides 325, affording the... 

The Au(III)-catalyzed double hydroamination cascade reaction of ortho-alkynyla-nilines 167 with terminal alkynes 168 affording N-vinylindoles 169 was reported by li (Scheme 9.63) [221]. In the case of alkyl-substituted acetylenes, this protocol provided mixtures of isomeric N-vinylindoles with both terminal and internal double bonds. This transformation is believed to occur via the Au(III)-catalyzed cydoisomerization of transient key alkynyl imines, similar to 162 utilized by Yamamoto, which were generated via the initial Au(111)-catalyzed hydroamination of the corresponding anilines 167 with alkynes 168. 

Nishina and Yamamoto have also reported the gold(I)allenes with alcohols [109]. As an example, treatment of a neat mixture of p-tolyl allene and isopropanol with a catalytic 1 1 mixture of (PPh3)AuCl and AgOTf at 30 °C led to isolation of isopropyl )-3-(4-tolyl)-2-propenyl ether in 98% yield (Eq. (12.39)). The protocol was most effective for monosubstituted and 1,3-disubstituted allenes and gave no transfer of chirality for the hydroalkoxylation of 1-phenyl-l,2-butadiene. Horino has reported the gold(I)-catalyzed intermolecular addition of alcohols to the allenyl moiety of 4-vinylidene-2-oxazolidinones [110]. 

Yamamoto reported another example of eyelisation of aminoallenes in 2006. This reaetion proeeeded in THF, at room temperature and it was mediated by gold(i)- gold(iii)-ehloride. This protocol allowed for the synthesis of five- or six-membered ring nitrogen heterocycles in good yields under very mild conditions (Scheme 16.55). 

Chiral Brpnsted acid catalysis of organic reactions has become a rapidly growing area of research, as it offers operational simplicity together with mild reaction conditions. However, the first Brpnsted acid-catalyzed 1,3-DC of diaryl nitrones 17 to ethyl vinyl ether 18 was demonstrated by Yamamoto and coworkers in 2008 [16]. Only 5 mol% of chiral phosphoramide catalyst 20 was enough for this transformation. Similar to some Lewis acid-catalyzed 1,3-DC reaction, this protocol provided the endo products as the major diastereomers (Scheme 2.7). 

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