Regio- and stereoselective synthesis of 2-amino-1,3-diene derivatives by ruthenium-catalyzed coupling of ynamides and ethylene

A ruthenium-catalyzed hydrovinylation-type cross-coupling of ynamides and ethylene proceeds via ruthenacyclopentene to give 2-aminobuta-1,3-diene derivatives in a highly regioselective manner. It was also demonstrated that 2-aminobuta-1,3-diene derivatives reacted with various dienophiles or singlet oxygen to give a cyclic enamide derivative.     

Regio- and stereoselective synthesis of alkyl allylic ethers via gold(I)-catalyzed intermolecular hydroalkoxylation of allenes with alcohols

Reaction of 1-phenyl-1,2-butadiene with 2-phenyl-1-ethanol catalyzed by a 1:1 mixture of a gold(I) N-heterocyclic carbene complex and AgOTf at room temperature for 1 h led to isolation of (E)-(3-phenethoxy-1-butenyl)benzene in 96% yield as a single regio- and stereoisomer. Gold(I)-catalyzed intermolecular allene hydroalkoxylation was effective for monosubsituted, 1,1- and 1,3-disubstituted, trisubstituted, and tetrasubstituted allenes and for a range of primary and secondary alcohols, methanol, phenol, and propionic acid.     

Syntheses of trifluoromethylated diene derivatives through the claisen rearrangement of trifluoromethylated propargylic and allylic alcohols

3-Trifluoromethyl-2Z, 4E-dienoate ($\text{14}$) and the dienamide ($\text{10}$,$\text{11}$) were prepared through the Claisen rearrangement of trifluoromethylated propargylic and allylic alcohols.     

Concise syntheses of nonracemic gamma-fluoroalkylated allylic alcohols and amines via an enantiospecific palladium-catalyzed allylic substitution reaction

Alpha-fluoroalkylated allyl mesylates reacted with various carboxylates and amines in the presence of tetrakis(triphenylphosphine)palladium(0) catalyst to give the corresponding gamma-fluoroalkylated (E)-allylic alcohol derivatives and amines, respectively, in excellent yields. In almost all cases, no other regio- and stereoisomers were produced. Application of this palladium-catalyzed allylic substitution reaction to various nonracemic mesylates afforded chiral gamma-fluoroalkylated allylic alcohol derivatives and amines without any loss of enantiomeric excess through the reaction.     

Low-valent titanium-mediated stereoselective alkylation of allylic alcohols

We have developed low-valent titanium-mediated 1,3-transpositive cross-coupling reactions of acyclic and cyclic allylic alcohols for the stereoselective introduction of ethyl, 2-silylethyl, 2-phenethyl, and alkenyl groups. Cross-coupling of an allylic alcohol with a vinylsilane or styrene derivative is particularly noteworthy, as an efficient cross-selective coupling of two alkenes has been elusive. The stereochemistry of the cross-coupling alkylation is consistent with syn addition/beta-elimination.     

Highly regioselective coupling reactions of allylic and propargylic alcohol derivatives with gamma,gamma-dialkoxyallylic zirconium species via Zr-to-Cu transmetalation

In the presence of CuCN, reaction of gamma,gamma-dialkoxyallylic zirconium species 4, generated in situ by treating triethyl orthoacrylate with zirconocene-butene complex, with allylic and propargylic phosphates proceeded at the alpha-position of 4 in a highly SN2'-selective manner to give the corresponding 5-alkenoates and 4,5-alkadienoates, respectively. In the present Cu(I)-mediated coupling reaction, the gamma,gamma-dialkoxyallylic zirconium species 4 serves as a synthetically useful homoenolate anion equivalent of propionate.     

Regioselective dehydroxytrifluoromethylthiolation of allylic and propargylic alcohols with AgSCF3

The reaction of easily available Morita–Baylis–Hillman (MBH) alcohols with AgSCF₃ in the presence of n-Bu₄NI and KI affords primary allylic SCF₃ products in high yields and excellent regioselectivities. This regioselective dehydroxytrifluoromethylthiolation protocol could also be extended to propargylic alcohols for the preparation of the primary propargylic SCF₃ products.     

Base-catalyzed stereoselective isomerization of electron-deficient propargylic alcohols to E-enones

We have developed highly stereoselective methods to isomerize electron-deficient propargylic alcohols to E-enones under mild conditions (EWG = electron-withdrawing group). Among weak bases we screened, catalytic (10-20 mol %) 1,4-diazabicyclo[2.2.2]octane (DABCO) was found to be effective in most cases. When the substrate is conjugated with an amide, the addition of sodium acetate catalyzed the isomerization.     

Regio- and stereoselective synthesis of tetrasubstituted allylic alcohols by three-component reaction of acetylenic sulfone, dialkylzinc, and aldehyde

(Z)-Tetrasubstituted allylic alcohols bearing sulfonyl group were synthesized regio- and stereoselectively by alkylzincation of acetylenic sulfone followed by addition to aldehyde.     

Regio- and stereoselective preparation of highly substituted tertiary homoallylic alcohols

The titanocene(II)-promoted reaction of α-(benzyldimethylsilyl)allylic sulfides with ketones proceeded with high regio- and stereoselectivity to give δ-silylhomoallylic alcohols. The following palladium catalyzed cross-couplings with organic halides produced anti-(E)-β,δ-disubstituted tertiary homoallylic alcohols with complete retention of configuration.     

Regio- and stereoselective synthesis of Z-vinylic tellurides from propargylic alcohols: a route to chiral Z-enynes

tert-Butyldimethylsilyl ethers of propargylic alcohols are hydrotellurated regioselectively to give 1,2-Z-vinylic tellurides. Enantiomerically pure propargylic alcohols give enantiomerically pure vinylic tellurides, which are coupled with alkynes under Pd catalysis to give enantiomerically pure allylic enynols.     

Efficient and stereoselective synthesis of allylic ethers and alcohols

[Structure: see text] A short and efficient synthesis of allylic TBS ethers and allylic alcohols has been developed, based upon a unique Kocienski-Julia olefination reaction. Allylic alcohols and allylic ethers are obtained in good to excellent yields and with high (E)-selectivity. The conditions are mild and the procedure is broadly applicable.     

Alkyne-aldehyde reductive C-C coupling through ruthenium-catalyzed transfer hydrogenation: direct regio- and stereoselective carbonyl vinylation to form trisubstituted allylic alcohols in the absence of premetallated reagents

Nonsymmetric 1,2-disubstituted alkynes engage in reductive coupling to a variety of aldehydes under the conditions of ruthenium-catalyzed transfer hydrogenation by employing formic acid as the terminal reductant and delivering the products of carbonyl vinylation with good to excellent levels of regioselectivity and with complete control of olefin stereochemistry. As revealed in an assessment of the ruthenium counterion, iodide plays an essential role in directing the regioselectivity of C-C bond formation. Isotopic labeling studies corroborate reversible catalytic propargyl C-H oxidative addition in advance of the C-C coupling, and demonstrate that the C-C coupling products do not experience reversible dehydrogenation by way of enone intermediates. This transfer hydrogenation protocol enables carbonyl vinylation in the absence of stoichiometric metallic reagents.     

Kinetic resolution of allylic alcohols via stereoselective acylation catalyzed by lipase PS-30

By using lipase PS-30 as catalyst, the kinetic resolution of a series of racemic allylic alcohols has been achieved via stereoselective acylation. The value of kinetic enantiomeric ratio (E) reached up to 968. Substituent effect is briefly discussed.     

Regio- and stereoselective oxetane formation via paterno-buchi photocycloaddition

Carbonyl 2 + 2 photoaddition occurs selectively to the alkene moiety of 3-(4-methyl-3-pentenoxy)pyridine. Photolysis of alkene containing pyridines in acetophenone gives rise to an oxetane which is obtained with extremely high diastereoselectivity as shown by analysis of the major 2 + 2 photoproduct. A second photoproduct, 2,3-dihydroxy-2,3-diphenylbutane, is obtained as a result of acetophenone coupling.     

Remarkable effect of N-substituent on enantioselective ruthenium-catalyzed propargylation of indoles with propargylic alcohols

Ruthenium-catalyzed enantioselective propargylation of indoles with propargylic alcohols affords the corresponding beta-propargylated indoles in good yields with a high enantioselectivity (up to 95% ee). A remarkable effect of the nature of the N-substituent of indoles is observed for the enantioselectivity of the propargylated indoles. The preparative method described in this paper may provide a novel protocol for asymmetric Friedel-Crafts alkylation of indoles using propargylic alcohols as a new type of electrophiles.     

Regio- and stereoselective homolytic hydrostannylation of propargyl alcohols and ethers with dibutylchlorostannane

The Et3B-initiated reaction of gamma-unsubstituted propargyl alcohols with dibutylchlorostannane (Bu2SnClH) at low temperature gave (Z)-vinylstannanes with high regio- and stereoselectivity. The corresponding alkyl propargyl ethers also underwent regio- and stereoselective homolytic hydrostannylation with Bu2SnClH; however, the regioselectivity was not so high as that with the propargyl alcohols.