1,6-Conjugate addition of para-quinone methides using gem-diborylcarbanions: Practical access to gem-diborylalkanes bearing vicinal tertiary/quaternary stereocenters

A novel,efficient and pragmatic method to prepare gem-diboron products with vicinal tertiary/quaternary stereocenters using LiTMP-mediated 1,6-conjugate addition of gem-diborylalkanes to para-quinone methides was described for the first time.The results showed that various gem-diboron products with vicinal tertiary and quaternary stereocenters could be formed within 15 min at ambient temperature.This simple protocol has also been applied for the efficient synthesis of the analogue of Bedaquiline.

Transition-metal-catalyzed switchable divergent cycloaddition of para-quinone methides and vinylethylene carbonates:Access to different sized medium-sized heterocycles

Divergent synthesis of medium-sized rings with controllable ring sizes represents a longstanding challenge in organic synthesis.Herein,we developed a transition-metal-catalyzed switchable divergent cycloaddition of para-quinone methides and vinylethylene carbonates by controlling the steric hindrance of substituent.Different from reported alkoxide-triggered annulations,this process undergoes a regiodivergent allylation of para-quinone methides followed by 1,6-addition reaction,providing a new route to selectively synthesize seven-to ten-membered nitrogen-containing heterocycles in high yields with excellent regioselectivities.This protocol features a broad substrate scope,wide functional group tolerance as well as operational simplicity.The reaction mechanism was investigated by conducting a series of control experiments as well as DFT calculations and the origins of the regioselectivities of the cycloaddition process were rationalized.

Photoinduced reaction of potassium alkyltrifluoroborates,sulfur dioxide and para-quinone methides via radical 1,6-addition

A photoinduced reaction of potassium alkyltrifluoroborates,sulfur dioxide,and para-quinone methides under visible light irradiation at room temperature is developed,giving rise to diarylmethyl alkylsulfones in moderate to good yields.This reaction works well under photocatalysis with a broad substrate scope by using DABCO·(SO_(2))_(2)as the source of sulfur dioxide.Mechanistic study shows that this transformation is initiated by alkyl radicals generated in situ from potassium alkyltrifluoroborates in the presence of photocatalyst.The subsequent insertion of sulfur dioxide and radical 1,6-addition of para-quinone methides with alkylsulfonyl radical intermediates afford the corresponding diarylmethyl alkylsulfones.

Visible light and base promoted O-H insertion/cyclization of para-quinone methides with aryl diazoacetates: An approach to 2,3-dihydrobenzofuran derivatives

A visible light and base promoted O-H insertion/cyclization of para-quinone methides with aryl diazoacetates is developed. This one-pot two step reaction offers a mild and efficient approach for the synthesis of biologically important 2,3-dihydrobenzofuran derivatives in good yields and moderate diastereoselectivities.

Synthesis of 9-phenol-substituted xanthenes by cascade O-insertion/1,6-conjugate addition of benzyne with ortho-hydroxyphenyl substituted para-quinone methides

The cascade O-insertion/1,6 conjugate addition between benzynes and ortho-hydroxyphenyl substituted para-quinone methides has been reported, affording 9-phenol substituted xanthenes in 49%-84% yields.

Transition-metal-free synthesis of 1,4-benzoxazepines via[4+3]-cycloaddition of para-quinone methides with azaoxyallyl cations

A formal[4+3]-cycloaddition reaction of ortho-hydroxyphenyl-substituted para-quinone methides(p-QMs)with in-situ generated azaoxyallyl cations is reported.The reaction occurs under very mild reaction conditions(transition-metal free,room temperature,cheap inorganic base)and provides a very efficient route to a series of biologically important 1,4-benzoxazepine derivatives in good to excellent yields.

Organocatalytic cascade 1,6-conjugate addition/annulation/tautomerization of functionalized para-quinone methides： Access to chiral 2-amino-4-aryl-4H-chromenes

A novel organocatalytic cascade process initiated by 1,6-conjugated addition has been successfully developed. A range of pharmaceutically active 2-amino-4-aryl-4H-chromenes were readily obtained in high yields（88%-99%） and excellent enantiopurities（86%-99% ee）. The functionalized para-Quinone methides（p-OMs） could be facilely obtained.

Diastereodivergent formal[4+1]cycloaddition of azoalkenes as one-carbon synthons

The first diastereodivergent formal[4+1]cycloaddition reactions of azoalkenes with p-quinone methides(pQMs)have been accomplished.The reported reaction occurred via a domino oxa-1,4-addition/1,6-addition process,allowing the use of common azoalkenes as C1 synthons.A broad range of 2,3-dihydrobenzofurans was smoothly prepared in good yields and with reversible diastereoselectivities.The steric hindrance and hydrogenbonding interaction were proposed to account for the two different modes of diastereo-control.The projected reaction features the employment of azoalkene as carbene-like C1 synthon,mild conditions,broad substrate scope and tunable diastereoselectivity.

Diastereoselective synthesis of spiro[chromane-3,30-indolines]and spiro[chromane-3,20-indenes]via DBU promoted formal[4+2]cycloaddition reaction

A new DBU-catalyzed formal[4+2]cycloaddition between ortho-hydroxyphenyl-substituted para-quinone methides and electron-deficient dienophiles including 3-methyleneoxindoles and 2-aryldeneindene-1,3-diones was established.A wide range of functionalized spiro[chromane-3,30-indolines]and spiro[chromane-3,20-indenes]were successfully synthesized in good yields and with high diastereoselectivity.The features of the reaction included readily available substrates,mild reaction conditions,convenient methodology and good functional group tolerance.