Samarium(II)-mediated reaction of allylic phosphate esters with carbonyl compounds: A new method for “Umpolung” of allylic phosphates

Allylic phosphates allylate ketones and aldehydes in the presence of samarium(II) iodide. The coupling proceeds with the preservation of the olefin geometry, however, regio- and stereoselectivity are not high.     

Iron-catalyzed esterification of allylic sp3 C–H bonds with carboxylic acids: Facile access to allylic esters

The first general and efficient iron-catalyzed esterification of allylic sp³ C–H bonds with carboxylic acids using ionic iron(III) complexes (1–4) as a catalyst and DTBP (DTBP = di-tert-butyl peroxide) as an oxidant is achieved. A variety of allylic esters were synthesized in good to excellent yields using the ionic iron(III) complex 2 as a catalyst in a 5 mol% loading. This reaction is characterized by its high efficiency, broad substrate scope with excellent steric hindrance tolerance and good functional group compatibility.     

Palladium-catalyzed selective heck-type diarylation of allylic esters with aryl halides involving a β-OAc elimination process

Palladium-catalyzed selective Heck-type diarylation of allylic esters with aryl halides has been developed. Allylic esters are reacted with aryl iodides to provide the corresponding 1,3-diaryl propenes through a β-OAc elimination process. It is noteworthy that the methodology can be applied in constructing the indole and benzofuran skeletons.     

Diastereoselectivity in the Carroll rearrangement of β-keto esters of tertiary allylic alcohols

Carroll rearrangement of β-keto esters derived from tertiary allylic alcohols, for example, 7, under basic conditions followed by decarboxylation of the resulting β-keto acids yielded the expected γ,δ-unsaturated methyl ketones 8 with a range of olefin geometries from 100:0 to 1:1.8 E/Z, depending on the relative steric requirements of the two groups at the allylic center.     

Ligand coupling through σ-sulfurane — complete retention of geometric configuration of allylic and vinylic groups in the reactions of allylic and vinylic sulfoxides with Grignard reagents

The reaction of p-benzenesulfonylphenyl crotyl sulfoxide with Grignard reagents is considered to proceed via formation of an incipient σ-sulfurane to afford the coupling product, p-benzenesulfonyl-crotylbenzene, in which the geometric configuration of crotyl group was completely preserved. No rearrangement was observed in the coupling reaction of p-benzenesulfonylphenyl α-methylallyl sulfoxide. Such a complete retention of geometric configuration was also found in the reactions of 2-pyridyl and p-benzenesulfonylphenyl styryl sulfoxides with Grignard reagents.     

SN2-Selective allylic substitution of chiral γ-aryl substituted allylic picolinates with alkynylcopper reagents

Substitution of γ-aryl secondary allylic picolinates with alkynyl copper reagents was studied. The copper reagent, prepared from TMSCCMgBr and CuBr·Me₂S in 2:1, was subjected to substitution of the picolinate derived from (E)-3-phenyl-1-methyl-2-propenyl alcohol at 0 °C for 1 h in THF to produce a mixture of α- and γ-products and the alcohol in 67:20:13, while the reagent in 3 or 4:1 ratio gave the α-product with 90-91% selectivity. On the contrary, reaction in CH₂Cl₂-THF (6-8:1) at 0 °C for 1 h furnished the α-product with 99% regioselectivity. The effect of CH₂Cl₂ was also demonstrated with eight more examples. Furthermore, 99% inversion was determined by transformation to the literature compound and by chiral HPLC.     

On the extent of racemization of allylic esters during palladium—mediated alkylation with homochiral 3-methyl-δ-butyrolactone derivatives

The allylic phosphate 4e has been shown to racemize 4̃–6% upon alkylation with the sodium lactone enolates of 1c and ent-1c in the presence of Pd(Ph₃P)₄. The acetate 4d racemizes 11%.     

The preparation of enantiomerically enriched γ-amino acids (GABAs) using palladium catalysed allylic substitution

Enantioselective palladium catalysed allylic substitution reactions have been employed as the asymmetry-producing step in the synthesis of enantiomerically enriched γ-amino acids.     

Photocatalytic aerobic cross-coupling reaction of N-substituted anilines with N-aryl glycine esters: Synthesis of α-aryl α-amino esters

A novel photocatalytic cross dehydrogenative coupling reaction of N-aryl glycine esters with N-substituted anilines has been developed. The reaction proceeds effectively using methylene blue as a photocatalyst under visible light irradiation without any metal, chemical oxidant or additive. A variety of α-aryl α-amino derivatives were prepared in moderate to excellent yields with a high para-regioselectivity.     

DMAP catalysed vinylogous Rauhut–Currier reaction of allenoates with para-quinone methides

The hitherto unknown, organocatalysed (DMAP) vinylogous Rauhut-Currier reaction of 2,3-butadienoates with para-quinone methides has been achieved. The products, diarylmethane substituted allenoates, are formed in high to excellent yields under mild reaction conditions.     

Stereochemistry of transition metal catalyzed asymmetric intramolecular allyl transfer in chiral α-sulfinyl allylic esters

The stereochemistry of palladium or nickel catalyzed asymmetric intramolecular allyl transfer in chiral α-sulfinyl allylic esters was determined. The participation of the catalyst and the chiral sulfinyl functionality in these transformations, presumably by the coordination of the sulfinyl group to the catalyst, is discussed, and a novel mechanism is proposed for the rationalization of the results obtained.     

Formal meta-specific intramolecular Friedel–Crafts allylic alkylation of phenols through a spirocyclization–dienone–phenol rearrangement cascade

Formal meta-specific intramolecular Friedel–Crafts allylic alkylation of phenols was achieved based on spirocyclization–dienone–phenol rearrangement cascades. Systematic screening of acid catalysts revealed that Sc(OTf)₃ was a highly effective catalyst for dienone–phenol rearrangement of spiro[4.5]cyclohexadienones. Using 5 mol % of Sc(OTf)₃ as the promoter, various spirocyclic substrates were transformed into the corresponding phenol derivatives in good to excellent yield. Furthermore, the one-pot sequential spirocyclization–dienone–phenol rearrangement proceeded using a palladium and scandium multi-catalytic system or a triphenylmethyl cation single-catalyst system, providing the corresponding meta-allylated phenol derivatives in excellent yield.     

Reactions of Tertiary Alcohols with Palladium(II) Tetraaqua Complex. Formation of Palladium π-Allyl Complexes

Transformations of 2-methyl-2-propanol, 2-methyl-2-butanol, 2-methyl-2-pentanol, 1-methyl-1-cyclohexanol, and 1-ethyl-1-cyclohexanol in the presence of tetraaquapalladium(II) ions in perchloric acid madium were studied. It was found that the reactions give rise to palladium(II) -allyl complexes. The reaction rate increases and the yield of the corresponding -allyl complex decreases with increasing hydrocarbon chain length. Addition of iron(III) ions to the systems essentially increases the yield of palladium -allyl complexes. The olefin formed from the corresponding tertiary alcohol participates in the formation of the palladium -allyl complex. Oxidation of 2-methyl-2-butanol with tetraaquapalladium(II) ions gives the isomeric palladium -allyl complexes [Pd(³-(CH₃)₂CCHCH₂)bpy]ClO₄ and [Pd(³-(CH₂C(CH₃)CHCH₃))bpy]ClO₄, which were isolated using 2,2'-bipyridyl and characterized by ¹H and ¹³C NMR spectroscopy.