Investigations of α-Siloxy−Epoxide Ring Expansions Forming 1-Azaspirocyclic Ketones
摘要:
The construction of 1-azaspirocyclic cycloalkanones using a siloxy-epoxide semipinacol ring expansion process was examined. Functionalized 1-azaspiro[5.5]undecan-7-ones (1-azaspirocyclic cyclohexanones) proceeded in high chemical yields with complete diastereoselectivity using titanium tetrachloride as the Lewis acid promoter. The formation of functionalized 6-azaspiro[5.4]-decan-1-ones (1-azaspirocyclic cyclopentanones) proceeded in high chemical yield with little diastereoselectivity. Modification of reaction parameters such as the Lewis acid promoter or the nature of the silyl ether allowed for the preferential formation of either ("anti" or "syn" 1,2 alkyl shift) diastereomeric product. An explanation for the different reactivity profiles between the cyclobutanol silyl ethers and cyclopentanol silyl ethers is provided.
Investigations of α-Siloxy−Epoxide Ring Expansions Forming 1-Azaspirocyclic Ketones
摘要:
The construction of 1-azaspirocyclic cycloalkanones using a siloxy-epoxide semipinacol ring expansion process was examined. Functionalized 1-azaspiro[5.5]undecan-7-ones (1-azaspirocyclic cyclohexanones) proceeded in high chemical yields with complete diastereoselectivity using titanium tetrachloride as the Lewis acid promoter. The formation of functionalized 6-azaspiro[5.4]-decan-1-ones (1-azaspirocyclic cyclopentanones) proceeded in high chemical yield with little diastereoselectivity. Modification of reaction parameters such as the Lewis acid promoter or the nature of the silyl ether allowed for the preferential formation of either ("anti" or "syn" 1,2 alkyl shift) diastereomeric product. An explanation for the different reactivity profiles between the cyclobutanol silyl ethers and cyclopentanol silyl ethers is provided.
Cracked under strain: Strained allylic cyclobutanols and cyclopropanols readily undergo a ring expansion described by the title rearrangement. This reaction is promoted by catalytic amounts of 1 and displays high tolerance with respect to the substrate scope. The corresponding β‐fluoro spiroketone products are isolated in high yields and with excellent stereoselectivities. EDG=electron‐donating group
the heavier halogens (bromine and iodine) second, the scope and limitations of the halogenative phase‐transfer methodology will be discussed and compared. An extension of the fluorination/semi‐pinacol reaction to the ring‐expansion of five‐membered allylic cyclopentanols will be also described, as well as some preliminary results on substrates prone to desymmetrization will be given. Finally, the present
A Mn(<scp>iii</scp>)/TEMPO-co-mediated tandem azidation–1,2-carbon migration reaction of allylic silyl ethers
作者:Zhi-Min Chen、Zhen Zhang、Yong-Qiang Tu、Ming-Hui Xu、Fu-Min Zhang、Chen-Chen Li、Shao-Hua Wang
DOI:10.1039/c4cc04707a
日期:——
A novel Mn(III)/TEMPO-co-mediated tandem azidation-1,2-carbon migration reaction of allylic silylethers with an unactivated C=C bond has been explored, generating alpha-aryl-alkyl beta-azido ketones with an alpha-quaternary stereocenter.
Electrochemical halogenation/semi-pinacol rearrangement of allylic alcohols using inorganic halide salt: an eco-friendly route to the synthesis of β-halocarbonyls
An efficient and eco-friendly electrochemical method involving halogenation/semi-pinacol rearrangement of allylic alcohols using inorganic halide salt as the halogen source to synthesize various β-halocarbonyls bearing an all-carbon α-quaternary center undermild reaction conditions has been developed (X = Br, Cl). Stoichiometric oxidants, metal catalysts, and even external electrolytes were avoided
A novel copper‐catalyzed tandem trifluoromethylation/semipinacol rearrangement reaction of allylic alcohols has been achieved under mild conditions. This reaction is valuable for the difunctionalization of alkenes through simultaneous construction of a CCF3 bond and a quaternary carbon center, and could provide a straightforward strategy for the preparation of α‐quaternary β‐trifluoromethyl ketone