Allylindium reagents

The use of allylindium reagent, generated in situ, makes it possible to introduce the allyl group into C-aromatic aldonitrones, in dimethylformamide DMF-H2O at room temperature (675). Under similar conditions the indium-catalyzed reaction of propargyl bromide with nitrones leads to the corresponding homoalkynyl hydroxylamines (Scheme 2.191) (676). 

Allylaziridines have been prepared in good yield by the action of allylindium reagents on azirines (e.g. 25).63 The C(3) substituent can control stereochemistry hydroxy- (or acetoxy-) -methyl gives d.v-allylalion (via chelation with the indium (g) reagent), whereas R = Me/Ph/C02Et gives a trans result, presumably due to steric repulsion. 

A three-component reaction based on the umpolung of re-allylpalladium (II) complexes indium metal was reported by Grigg and co-workers (Scheme 8.31) [74]. In this reaction, the electrophilic nature of the n-allyl palladium species generated from aryl halides and allenes is reversed by transmetallation with indium metal. The resultant nucleophilic allylindium reagent subsequently adds to the third component - aldehyde [75] or imine [76] - to give the corresponding homo-allylic alcohol 64 or amine 65 respectively. 

Oxozirconocenes, preparation, 4, 916—917 7-Oxygenated allylindium reagents, in carbonyl allylations,... 

Allylindium reagents bearing substituents at the 7-position react with carbonyl compounds in organic and aqueous media regioselectively at the 7-position, via a six-membered transition state, to afford the corresponding branched homoallylic alcohols, if no sterically bulky carbonyl or allyl substituent is involved.102 For example, the indium-mediated reaction of aldehydes with 3-bromo-l-cyano-l-propene proceeds readily in water to give cr-cyano-f3-ethylenic secondary alcohols (Scheme 4).103... 

The reactions involving sulfur derivatives are minimally diastereoselective, indicating that the allylindium reagent is not thiophilic (Table 3).159 The modest levels of diastereoselectivity observed in all the sulfur examples, which are... 

Pan et al. reported similar reactions of / -quinones to 4-allyl-4-hydroxycyclohexa-2,5-dienone derivatives (Equation (26)).194 Unsymmetrical quinones show high selectivity in the addition of allylindium reagents to the carbonyl group. Indium-mediated allylation of 1,2-diones occurs via a y-coupling fashion to yield ct-hydroxy keto compounds. In some cases of cinnamylation, the corresponding a-coupling products are obtained (Equation (27)).195,196... 

The coupling reaction of allylindium reagents with cyclic imides gives diverse products depending on the structure of both the substrates and the reagents (Scheme 49).206... 

Treatment of acyl phosphates with allylindium reagents in the presence of acetic acid affords the corresponding a-hydroxy phosphonates in good yields under mild conditions (Equation (52)).240 (3-Keto phosphonates give the corresponding / -hydroxy phosphonates in good yields by indium-mediated allylations (Equation (53)).241... 

The allylation of imines with allylindium reagents in organic solvents gives the corresponding homoallylic amines.251-253 Under solvent-free conditions, the indium-mediated reaction of iV-benzylideneaniline furnishes a mixture of mono-allylated 79 and bis-allylated products 80 (Equation (56)). The bis-allylated product 80 presumably arises via a formation of an iminium salt, which is subsequently attacked by the allylindium nucleophiles. Formation of 80 is entirely suppressed by addition of allyl bromide to indium metal prior to any addition of the imine (Grignard-type reaction).254... 

Allyl and benzyl bromides react with a,/ -unsaturated nitriles in the presence of indium(i) iodide under sonication to produce the corresponding allylated and benzylated imines, involving exclusive addition of the allyl/benzyl group to the nitrile moiety (Equation (63)).273 The reaction of allylindium reagents with methyl cyanoacetates affords the corresponding allylation-enamination products (Equation (64)).27 l-Acyl-l,2-dihydropyridines are prepared by indium-mediated allylation of 1-acylpyridinium salts (Equation (65)).275 Quinoline and isoquinoline activated by... 

Allylmetallation of alkynes is a useful tool for the synthesis of 1,4-dienes. Various main group allylmetals, as well as allylic transition metals, have been utilized in such transformations. The reaction of allylindium reagents with terminal alkynols was first reported in 1992. The reaction proceeds in DMF giving 1,4-dienes, where the proximal... 

A-allylic amines are conveniently prepared in high yields by the reaction of azides with allylindium reagents in the presence of sodium iodide at ambient temperature (Equation (74)).307 Stannylation with tributylchloro-stannane occurs exclusively at the a-carbon, yielding allyltributylstannanes (E, Z)-isomerization of the allylic double bond depends largely upon the substitution pattern on the allylic moiety (Equation (75)).26 Allyl and propargyl bromides react with diphenyl diselenides in aqueous media to give allyl and propargyl selenides (Equation (76)).308 309... 

The reactions of allylindium reagents with trifluoroacetaldehyde hydrate or hemiacetal in water (Equation (79)), or with aldehyde dimethyl acetals in aqueous THF, give the corresponding homoallylic alcohols (Equation (80)). 313-315... 

Indium-mediated allylation of a nitro group is achieved in aqueous media to give A,A-diallylamine and 7V,0-diallylhydroxylamine (Equation (81)) 316 In situ generated sulfonium salts derived from a,/3-enones undergo a nucleophilic substitution with allylindium reagents to give the corresponding Michael addition products (Scheme 83).317... 

Indium-mediated allylation of 4-acetoxy-2-azetidinones affords 4-allyl-substituted azetidinones with retention of the stereochemistry (Equation (82)).320 An aminoalkoxy titanium complex is readily allylated with allylindium reagents to give homoallylic amines (Scheme 86).321... 

Allylindium reagents can be utilized in the Pd-catalyzed cross-coupling reaction with aryl halides. The Pd-catalyzed allylic substitution of allyl carbonate produces 1,5-dienes (Scheme 103).353-355... 

Scheme 11 Allylindation of cyclopropenes using allylindium reagents...

While y-selectivity is usually 4-chloro-2-butenyl benzyl ether the derived allylindium reagent a An intramolecular reaction ih... 

While y-selectivity is usually observed in reaction with substituted allyl halides (e.g., 4-chloro-2-butenyl benzyl ether"), 3-bromo-3,3-difluoro-l-propene behaves differently as the derived allylindium reagent adds to aldehydes like a,ot-difluoroallyl carbanion. ... 

The diastereoselective production of homoallylic indium alkoxides can be accomplished by a kinetic resolution process [194]. The indium-mediated reaction of benzaldehyde with 2-butenyl bromide has always been observed to be unselec-tive. The use of alkoxide or halide modifiers in the reactions of allylindium reagents has previously been shown to provide synthetically useful reagents [195], Upon addition of 2-butenylindium sesquibromide to benzaldehyde it was determined that newly formed syn and anti homoallylic alcohols undergo decomposition at a similar rate, but as the concentration of the anti homoallylic alcohol reaches zero, the rate of decomposition of the syn alcohol slows dramatically. Thus, the syn homoallylic alcohol can be obtained in high diastereoselectivity, albeit low yield. 

Achiral allylic indium reagents and chiral aldehydes. Allylindium reagents generated in water react smoothly with aldehydes and ketones (Scheme 10-99) [196], The reaction of achiral aldehydes and a-oxygenated aldehydes 290 with the allyl indium reagents proceeds smoothly to homoallylic alcohols without the need for external promoters. It is interesting to note that the a-hydroxyl aldehyde was se-leetive for the syn (chelation-eontrolled) product even in water. 

From an extensive examination of the addition of allylindium reagents to a-oxygenated aldehydes 291 it has been established that the stereochemical outcome is dependent on both the a-alkoxy substituent and the solvent employed (Table 10-33) [197]. The silyl and benzyl ethers favor the formation of the anti homoallylic alcohol, whereas the MOM and the hydroxyl aldehydes favor the syn alcohol. The rate of the reaction is dependent upon the solvent (faster in a mixed THF/water solvent) and the pH (faster at lower pH). 

---