“…Under the reaction conditions shown in Scheme 13, the b-CF 3 -substituted secondary (R)-allylic alcohol bearing ab romophenyl moiety (97 % ee)w as fully converted into the saturated (R)-ketone [94 % ee;E q. (22)]. [70] Thes ynthetic protocol provides an alternative route to the asymmetric synthesis of the CF 3 analogues of citronellol.…”
Section: Methodsmentioning
confidence: 99%
“…Carbon-carbon bond formation by means of efficient, selective,a nd environmentally benign processes has been achallenging task in synthetic chemistry. a-Alkylation of the enolates of ketones with electrophilic alkylating agents was documented to construct aC À Cbond, [7,21,22] but this protocol suffers from the production of stoichiometric amounts of undesirable salts as waste.In2001, Shim, Cho,and co-workers reported ruthenium-catalyzed transfer hydrogenation of ketones with primary alcohols accompanied by CÀCb ond formation. [23] Later,C ho documented the ruthenium-catalyzed b-alkylation of secondary alcohols with primary alcohols.…”
Section: Transition-metal-catalyzed C-alkylation Of Ketones and Seconmentioning
Transition-metal-catalyzed C-alkylation of ketones and secondary alcohols, with alcohols, avoids use of organometallic or environmentally unfriendly alkylating agents by means of borrowing hydrogen (BH) or hydrogen autotransfer (HA) activation of the alcohol substrates. Water is formed as the only by-product, thus making the BH process atom-economical and environmentally benign. Diverse homogeneous and heterogeneous transition-metal catalysts, ketones, and alcohols can be used for this transformation, thus rendering the BH process promising for replacing those procedures that use traditional alkylating agents. This Minireview summarizes the advances during the last five years in transition-metal-catalyzed BH α-alkylation of ketones, and β-alkylation of secondary alcohols with alcohols. A discussion on the application of the BH strategy for C-C bond formation is included.
“…Under the reaction conditions shown in Scheme 13, the b-CF 3 -substituted secondary (R)-allylic alcohol bearing ab romophenyl moiety (97 % ee)w as fully converted into the saturated (R)-ketone [94 % ee;E q. (22)]. [70] Thes ynthetic protocol provides an alternative route to the asymmetric synthesis of the CF 3 analogues of citronellol.…”
Section: Methodsmentioning
confidence: 99%
“…Carbon-carbon bond formation by means of efficient, selective,a nd environmentally benign processes has been achallenging task in synthetic chemistry. a-Alkylation of the enolates of ketones with electrophilic alkylating agents was documented to construct aC À Cbond, [7,21,22] but this protocol suffers from the production of stoichiometric amounts of undesirable salts as waste.In2001, Shim, Cho,and co-workers reported ruthenium-catalyzed transfer hydrogenation of ketones with primary alcohols accompanied by CÀCb ond formation. [23] Later,C ho documented the ruthenium-catalyzed b-alkylation of secondary alcohols with primary alcohols.…”
Section: Transition-metal-catalyzed C-alkylation Of Ketones and Seconmentioning
Transition-metal-catalyzed C-alkylation of ketones and secondary alcohols, with alcohols, avoids use of organometallic or environmentally unfriendly alkylating agents by means of borrowing hydrogen (BH) or hydrogen autotransfer (HA) activation of the alcohol substrates. Water is formed as the only by-product, thus making the BH process atom-economical and environmentally benign. Diverse homogeneous and heterogeneous transition-metal catalysts, ketones, and alcohols can be used for this transformation, thus rendering the BH process promising for replacing those procedures that use traditional alkylating agents. This Minireview summarizes the advances during the last five years in transition-metal-catalyzed BH α-alkylation of ketones, and β-alkylation of secondary alcohols with alcohols. A discussion on the application of the BH strategy for C-C bond formation is included.
“…Attempted alkylation of (-)- 75 with LDA followed by addition of excess MeI, under a variety of reaction conditions, led to mixtures of 76α and 76β and 74 along with unreacted (-)- 75 , even when excess of LDA was used. Reasoning that diisopropyl amine could enhance the proton exchange between the starting lactone enolate and 76α/β leading to epimerization and polyalkylation, 34 we decided to use the more hindered and stronger base Li-TMP, which is known to reduce the formation of aggregates. 35 Our hypothesis was confirmed when complete conversion of 75 was observed and a kinetically controlled mixture of 76 ( 76α / 76β ~1:1.5) was isolated in 75% yield accompanied by only traces of 77 .…”
A full account of studies that culminated in the total synthesis of both antipodes and the assignment of its absolute configuration of Saudin, a hypoglycemic natural product. Two approaches are described, the first proceeding though bicyclic lactone intermediates and related second monocyclic esters. The former was obtained via asymmetric Diels-Alder cycloaddition and the latter by an asymmetric annulation protocol. Both approaches employ a Lewis acid promoted Claisen rearrangement, with the successful approach taking advantage of bidentate chelation to control the facial selectivity of the key Claisen rearrangement
“…Sharpless dihydroxylation [8] of the latter gave the expected γ,δ-dihydroxy ester, which then spontaneously cyclized to 11. Protection as the TBS (t-butyldimethylsilyl) derivative was followed by αallylation via the lithium enolate [9]. The reaction took place with a very good stereoselectivity and provided lactone 10 as a 92:8 diastereomeric mixture (83% yield of 10 after chromatographic separation).…”
A stereoselective synthesis of the nonnatural enantiomers of the fungal metabolites communiols A-C is reported. A stereochemical misassignment has been corrected and the absolute configurations of the natural products have been unambiguously established.
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