Iron-Catalyzed Highly Regio- and Stereoselective Conjugate Addition of 2,3-Allenoates with Grignard Reagents

An efficient highly regio- and stereoselective iron-catalyzed conjugate addition of 2,3-allenoates with primary or secondary alkyl, phenyl, or vinyl Grignard reagents to synthesize multi-substituted β,γ-unsaturated enoates has been reported. The in situ formed magnesium dienolate may readily react with different electrophilic reagents to construct an allylic quaternary carbon at the α-position of the ester group

Iron-Catalyzed Unexpected Easy Access to Stereodefined Trimethylsilyl Vinyl Ketenes

Stereodefined trimethylsilyl vinyl ketenes with polysubstitution have been synthesized highly regio- and stereoselectively via an iron-catalyzed reaction of 2-trimethylsilyl-2,3-allenoates with Grignard reagents in good to excellent yields. The reaction was believed to proceed via a conjugate addition and elimination mechanism. Applications of the products for the synthesis of stereodefined α-silyl-β,γ-unsaturated enones, a stereodefined triene, and polysubstituted phenols have been carefully demonstrated

Controllable Highly Stereoselective Reaction of <i>in situ</i> Generated Magnesium Dienolate Intermediates with Different Electrophiles

In this paper, we have described an efficient controllable stereoselective α-acylation and -allylation reaction of the magnesium dienolate intermediates generated in situ from the Fe(III)-catalyzed reaction between 2,3-allenoates and Grignard reagents with different electrophiles to afford 2-acylated or allylated 3(Z)- or (E)-alkenoates depending on the nature of the electrophiles and reaction conditions. The distinct stereoselectivity may be caused by the isomerization of metallic Z-1,3-dienoate to E-1,3-dienoate via the intermediacy of anti-allylic MgCl and syn-metallic species

Efficient Assembly of Chromone Skeleton from 2,3-Allenoic Acids and Benzynes

Chromone derivatives were synthesized from 2,3-allenoic acids and benzynes in moderate to excellent yields under mild conditions. Instead of the cyclic conjugate addition of the intermediate A formed by the nucleophilic addition of allenoic acid with benzyne, this intermediate undergoes 1,2-addition with the carbonyl group, which was followed by the ring opening, conjugate addition, and protonolysis to afford chromone derivatives. This protocol allows the diversity due to the substituent-loading capability of 2,3-allenoic acids as well as benzynes

Electronic Effect Directed Au(I)-Catalyzed Cyclic C2–H Bond Functionalization of 3-Allenylindoles

Gold-catalyzed cyclization reactions of indoles with an electron-deficient allene at the 3-position led to formation of dihydrocyclopenta[b]indole derivatives in moderate to excellent yields via C2–H bond functionalization of the indole unit. The presence of the electron-withdrawing alkoxycarbonyl, dialkoxyphosphono, or phenyl is crutial for this transformation. The potential synthetic dihydrocyclopenta[b]indole with the electron-withdrawing group has been demonstrated by applying a [3 + 2] cycloaddition reaction to construct the tretracycloskeleton

Electronic Effect Directed Au(I)-Catalyzed Cyclic C2–H Bond Functionalization of 3-Allenylindoles

Gold-catalyzed cyclization reactions of indoles with an electron-deficient allene at the 3-position led to formation of dihydrocyclopenta[<i>b</i>]indole derivatives in moderate to excellent yields via C2–H bond functionalization of the indole unit. The presence of the electron-withdrawing alkoxycarbonyl, dialkoxyphosphono, or phenyl is crutial for this transformation. The potential synthetic dihydrocyclopenta[<i>b</i>]indole with the electron-withdrawing group has been demonstrated by applying a [3 + 2] cycloaddition reaction to construct the tretracycloskeleton

A Straightforward Synthesis of Cyclobutenones via a Tandem Michael Addition/Cyclization Reaction of 2,3-Allenoates with Organozincs

An efficient method for synthesis of polysubstituted cyclobutenones, which are not readily available from traditional methods due to the intrinsic ring strain, is described. The reaction of 2,3-allenoates and organozinc reagents proceeds via a tandem Michael addition/cyclic 1,2-addition/elimination mechanism with the functional groups from the organozinc reagents being introduced to the 3-position of the cyclobutenone products regiospecifically in moderate to excellent yields. Application to the synthesis of stereodefined β,γ-unsaturated enones is demonstrated

Efficient Assembly of Chromone Skeleton from 2,3-Allenoic Acids and Benzynes

Chromone derivatives were synthesized from 2,3-allenoic acids and benzynes in moderate to excellent yields under mild conditions. Instead of the cyclic conjugate addition of the intermediate A formed by the nucleophilic addition of allenoic acid with benzyne, this intermediate undergoes 1,2-addition with the carbonyl group, which was followed by the ring opening, conjugate addition, and protonolysis to afford chromone derivatives. This protocol allows the diversity due to the substituent-loading capability of 2,3-allenoic acids as well as benzynes

A Straightforward Synthesis of Cyclobutenones via a Tandem Michael Addition/Cyclization Reaction of 2,3-Allenoates with Organozincs

An efficient method for synthesis of polysubstituted cyclobutenones, which are not readily available from traditional methods due to the intrinsic ring strain, is described. The reaction of 2,3-allenoates and organozinc reagents proceeds via a tandem Michael addition/cyclic 1,2-addition/elimination mechanism with the functional groups from the organozinc reagents being introduced to the 3-position of the cyclobutenone products regiospecifically in moderate to excellent yields. Application to the synthesis of stereodefined β,γ-unsaturated enones is demonstrated

A Straightforward Synthesis of Cyclobutenones via a Tandem Michael Addition/Cyclization Reaction of 2,3-Allenoates with Organozincs

An efficient method for synthesis of polysubstituted cyclobutenones, which are not readily available from traditional methods due to the intrinsic ring strain, is described. The reaction of 2,3-allenoates and organozinc reagents proceeds via a tandem Michael addition/cyclic 1,2-addition/elimination mechanism with the functional groups from the organozinc reagents being introduced to the 3-position of the cyclobutenone products regiospecifically in moderate to excellent yields. Application to the synthesis of stereodefined β,γ-unsaturated enones is demonstrated