Homoallylic derivatives coupling

Iridium-catalyzed transfer hydrogenation of aldehyde 73 in the presence of 1,1-dimethylallene promotes tert-prenylation [64] to form the secondary neopentyl alcohol 74. In this process, isopropanol serves as the hydrogen donor, and the isolated iridium complex prepared from [Ir(cod)Cl]2, allyl acetate, m-nitrobenzoic acid, and (S)-SEGPHOS is used as catalyst. Complete levels of catalyst-directed diastereoselectivity are observed. Exposure of neopentyl alcohol 74 to acetic anhydride followed by ozonolysis provides p-acetoxy aldehyde 75. Reductive coupling of aldehyde 75 with allyl acetate under transfer hydrogenation conditions results in the formation of homoallylic alcohol 76. As the stereochemistry of this addition is irrelevant, an achiral iridium complex derived from [Ir(cod)Cl]2, allyl acetate, m-nitrobenzoic acid, and BIPHEP was employed as catalyst (Scheme 5.9). 

Exciton coupling is also observed in methacrylate derivatives of allylic alcohols151 and in a benzoate derivative of a homoallylic alcohol152. For benzoates of propargylic alcohols of S configuration 11 in which the O-Bz bond is assumed anti to the C-R1 bond, a Dc Voe calculation predicts a positive benzoate Cotton effect, in accordance with experimental153. 

In the context of the development of enzymatic methods for the synthesis of higher-carbon sugars we recently developed a new strategy by which dodeca-2,11-diuloses — formally derived from ketohexoses by C-coupling tail to tail — become accessible with deliberately addressable substitution patterns by the twofold aldolase-catalyzed chain elongation ( tandem aldolization) of simple, readily available dialdehydes [207]. The choice of furanoid (179) or pyranoid (180) nature of the products can be determined by a suitable placement of hydroxyl substituents in the allylic (181) or homoallylic ( 182) positions of a corresponding cycloolefinic precursor. 

A wide variety of silyl ethers can be employed, leading to functionalized homo-allylic alcohols or ethers. This three-component coupling reaction, which generates in a single operation a range of homoallylic ethers, does not require the initial and independent synthesis of the acetal (or ketal) derived from 6. 

A stereochemical study of the synthesis of unsaturated 1,4-aminoalcohols via the reaction of unsaturated 1,4-alkoxyalcohols with chorosulfonyl isocyanate revealed a competition between an retentive mechanism and an SnI racemization mechanism, with the latter having a greater proportion with systems where the carbocation intermediate is more stable.254 An interrupted Nazarov reaction was observed, in which a nonconjugated alkene held near the dienone nucleus undergoes intramolecular trapping of the Nazarov cyclopentenyl cation intermediate.255 Cholesterol couples to 6-chloropurine under the conditions of the Mitsunobu reaction the stereochemistry and structural diversity of the products indicate that a homoallylic carbocation derived from cholesterol is the key intermediate.256 l-Siloxy-l,5-diynes undergo a Brpnsted acid-promoted 5-endo-dig cyclization with a ketenium ion and a vinyl cation proposed as intermediates.257... 

Asymmetric Coupling Reactions of Chiral Grignard Reagents Derived from Ephedrine Derivatives. Asymmetric coupling reactions of Allyl Bromide and chiral Grignard reagents derived from ephedrine methyl ether in the presence of Copper(I) Iodide (10 mol %) followed by oxidation affords optically active homoallyl alcohols with 60% ee (eq 12). ... 

The intermolecular coupling of homoallyl alcohols with o-bromoacetophenone 127 (Scheme 3-33) or o-bromostyryl ketones 129 (Scheme 3-34) gave dihydro- 128 and tetrahydronaphtlialene derivatives 130 in a sequence of Heck and aldol or Heck and Michael reactions [185]. After addition of the arylpalladium species formed initially... 

Allylic halides are not as readily accessible as allylic alcohols or their ester derivatives. Thus, the requirement that allylic halides must be used as precursors for carbonyl addition reactions in conjunction with magnesium and other similar reductants is a severe restriction limiting the convenience of these routes to homoallylic alcohols. In this regard, samarium diiodide can be used to great advantage, because substrates other than allylic halides are suitable precursors for such transformations. For example, allylic phosphate esters have been reported to couple with carbonyl substrates in the presence of Smh (equation 15). Since esters and nitriles are unreactive under these conditions, the Smh-mediated process is likely to be more chemoselective than those promoted by magnesium or lithium. 

Formaldehyde can be coupled to an alkene in the presence of an acid to give a diol (152) or a 1,3-dioxane derivative (154) in what is known as the Prins reaction. l Allylic alcohols such as 153 can also be produced in this reaction. Camphene (155) reacted with formaldehyde and acid to give a 1 1 mixture of allylic alcohol 156 and the acetate 157, in 94% yield. Scandium tiiflate has been used to prepare tetrahydropyran-4-ol derivatives from aldehydes and homoallylic alcohols via a Prins-type cyclization. 3... 

Homoallyl bromide 314, prepared from readily available non-racemic ester 313, was converted to the Grignard reagent, which reacted with non-racemic epoxide, derived from D-maUc acid, to afford the alcohol 305. Ozonolysis of the alkene gave a ketone, which was converted into enol tri-flate 316. Ni-catalyzed cross coupling with trimethylsilylmethyl magnesium chloride afforded the allyl silane, which was converted into the allyl stan-nane 317. The asymmetric allylation of 313 with 317 provided 304 with a ration of 8.5 1. Methyl etherification and oxidative cleavage of exo-methylene... 

Homoallylic, /hh, and allylic couplings, Vhh, have been used by Gao et to elucidate the structure of (4i , 5S, 65, 85, 137 )-1-(2,8-dihydroxy- 1,2.6-trimethyl-1,2,6,7,8,8a-hexahydro-naphtalen-1 -yl)-3-meth-oxy-propan-l-one, a polyketide-originated metabolite isolated from a marine sponge-derived fungus Mycelia sterilia. 

Three-component coupling of 1 with 1,3-dienes and aldehydes proceeds in the presence of a platinum catalyst, giving boryl-substituted homoallylic alcohol derivatives in good yields with high diastereoselectivities (eq 22). This reaction is not considered to be a stepwise silaboration/allylation sequence, but catalytic allylplatination of the aldehyde. 

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