3695-38-3Relevant articles and documents
Enantioselective synthesis of the apple aroma constituent 1,3,3-trimethyl-2,7-dioxabicyclo[2.2.1]heptane via asymmetric dihydroxylation
Brimble,Rowan,Spicer
, p. 1263 - 1266 (1995)
The enantiomers of 1,3,3-trimethyl-2,7-dioxabicyclo[2.2.1]heptane (1) were prepared in two steps from 6-methylhept-5-en-2-one using Sharpless asymmetric dihydroxylation.
Half-Sandwich Ruthenium Carbene Complexes Link trans-Hydrogenation and gem-Hydrogenation of Internal Alkynes
Guthertz, Alexandre,Leutzsch, Markus,Wolf, Lawrence M.,Gupta, Puneet,Rummelt, Stephan M.,Goddard, Richard,Farès, Christophe,Thiel, Walter,Fürstner, Alois
, p. 3156 - 3169 (2018/03/08)
The hydrogenation of internal alkynes with [Cp?Ru]-based catalysts is distinguished by an unorthodox stereochemical course in that E-alkenes are formed by trans-delivery of the two H atoms of H2. A combined experimental and computational study now provides a comprehensive mechanistic picture: a metallacyclopropene (??2-vinyl complex) is primarily formed, which either evolves into the E-alkene via a concerted process or reacts to give a half-sandwich ruthenium carbene; in this case, one of the C atoms of the starting alkyne is converted into a methylene group. This transformation represents a formal gem-hydrogenation of a ?€-bond, which has hardly any precedent. The barriers for trans-hydrogenation and gem-hydrogenation are similar: whereas DFT predicts a preference for trans-hydrogenation, CCSD(T) finds gem-hydrogenation slightly more facile. The carbene, once formed, will bind a second H2 molecule and evolve to the desired E-alkene, a positional alkene isomer or the corresponding alkane; this associative pathway explains why double bond isomerization and over-reduction compete with trans-hydrogenation. The computed scenario concurs with para-hydrogen-induced polarization transfer (PHIP) NMR data, which confirm direct trans-delivery of H2, the formation of carbene intermediates by gem-hydrogenation, and their evolution into product and side products alike. Propargylic aOR (R = H, Me) groups exert a strong directing and stabilizing effect, such that several carbene intermediates could be isolated and characterized by X-ray diffraction. The gathered information spurred significant preparative advances: specifically, highly selective trans-hydrogenations of propargylic alcohols are reported, which are compatible with many other reducible functional groups. Moreover, the ability to generate metal carbenes by gem-hydrogenation paved the way for noncanonical hydrogenative cyclopropanations, ring expansions, and cycloadditions.
Facile entry to substituted decahydroquinoline alkaloids. Total synthesis of lepadins A-E and H
Pu, Xiaotao,Ma, Dawei
, p. 6562 - 6572 (2007/10/03)
Condensation of a L-alanine derived δ-bromo-β-silyloxy- propylamine with 1,3-cyclohexadione followed by alkylative cyclization produces a bicyclic enone. Diastereoselective Pt/C-catalyzed hydrogenation of this enone in HOAc provides a 5-oxo-cis-fused decahydroquinoline. Wittig olefination of this decahydroquinoline and subsequent epimerization of the resulting 5-formyl intermediate gives rise to a 5-β-formyl decahydroquinoline exclusively. In a parallel procedure, Peterson reaction of this decahydroquinoline and subsequent hydrogenation of the generated 5-exo-olefin provides a decahydroquinoline with a 5-α-substituent predominantly. For these two diastereoselective processes, using the intermediates without N-protection as the substrates is essential because the corresponding N-Boc intermediates give poor diastereoselectivity. The intermediate with β-form side chain is further converted into lepadins A-C via carbon chain elongation, while the intermediate with α-form side chain is transformed into lepadins D, E, and H and corresponding 5′-epimers via connection with two sulfones generated from two Sharpless epoxidation products. By comparison of the rotations and NMR data, the stereochemistry of lepadins D, E, and H is assigned as 2S,3R,4aS,5S,8aR,5′R.
Microwave assisted facile synthesis of Elvirol, Curcuphenol and Sesquichamaenol using Montmorillonite K-10 clay in dry media
Singh, Vasundhara,Khurana, Anupam,Kaur, Irvinder,Sapehiyia, Varinder,Kad, Goverdhan L.,Singh, Jasvinder
, p. 1766 - 1768 (2007/10/03)
Short, simple and convergent syntheses of the title compounds have been accomplished with good overall yields using a Montmorillonite K-10 clay catalyzed Friedel-Crafts alkylation reaction in 'dry media' as the key step.
