Tritylketone und Tritylenone. Beiträge zur sterisch erzwungenen Michael‐Addition und zur diastereoselektiven Aldol‐Addition

Abstract

Tritylketones are prepared from trityllithium and aldehydes, with subsequent CrO, oxidation (Scheme 1, 2a-f). Tritylenones are obtained from the saturated ketones and aldehydes or ketones, preferably by (CH3),Al-mediated aldol addition with subsequent dehydration (Scheme 2, products 2e, 4b-e). The carbonyl of the tritylketone group is sterically protected, but electronically effective (see A-C); thus, amine-free enolate solutions can be obtained directly with BuLi; also, exclusive conjugate addition of organolithium derivatives occurs with tritylenones (Srhemes 3-5, products Zd, 57, 15 examples). The lithiumenolates of tritylketones add to aldehydes with practically complete stereoselectivity (Scheme 6, products 10,9 examples): due to the bulkiness of the trityl group, only the (Z)-enolates 8 are formed, and the approach of the two trigonal centers in the aldol-addition step is enforced to occur with relative topicity ul. As a first example of an X-ray structure determination of a silyl enol ether, the crystal structure of (Z)-2-(trimethylsilyloxy)-l,l,l-triphenyl-2-butene (9) is reported. Fortunately, the blocking of the carbonyl group in trityl ketones can be run very specifically (without epimerization at the a-carbonyl center) by lithium triethylborohydride to furnish, after aqueous workup, primary alcohols and Ph3CH (Eqn. 4, products &20, 10 examples); the OH-group of the aldols 10 must be EE-, MOM-or MEM-protected (Scheme 8) before this C,C-bond cleavage can be conveyed. Some of the cleavage products are used for the chemical correlation of the aldol configuration and for the demonstration of the synthetic value of the presented method (see [21][22][23][24][25][26][27][28][29]

Electronic and Steric Control in Regioselective Addition Reactions of Organolithium Reagents with Enaldimines

“…It was further and considerable progress to extend this trick to a 1,4-selective addition reaction of organolithium reagents with a naphthalene nucleus. , Steric modification in a carbonyl moiety has been proven as an alternative methodology effective for a 1,4-selective conjugate addition of organolithium reagents . Pioneering works by Seebach and Cooke have demonstrated that sterically hindered α,β-unsaturated trityl ketones and BHA esters serve as the Michael acceptors, affording the corresponding 1,4-selective addition products . The BHA method was also extended to a 1,4-selective addition reaction of a naphthalenecarboxylate. , Steric masking and nucleophilic activation of naphthalenyl ketone by an external aluminum-based bulky Lewis acid has been impressive advance of 1,4- and 1,6-selective addition reactions .…”

“…3,4 Steric modification in a carbonyl moiety has been proven as an alternative methodology effective for a 1,4-selective conjugate addition of organolithium reagents. 5 Pioneering works by Seebach 6 and Cooke 7 have demonstrated that sterically hindered R,β-unsaturated trityl ketones and BHA esters serve as the Michael acceptors, affording the corresponding 1,4-selective addition products. 8 The BHA method was also extended to a 1,4-selective addition reaction of a naphthalenecarboxylate.…”

Catalytic Generation of Arynes and Trapping by Nucleophilic Addition and Iodination

“…[18] A precaution for the reaction of indenyllithium was to maintain the temperature (< À60 8C), otherwise a shift of the double bond occurred. The lithium enolate 25 [19] also worked nicely. Upon treatment of iodo triflate 7 in the presence of LiC CSiMe 3 (10 mol %, À78!…”

Stereospecific 1,4-Addition of Organolithium Reagents to Unprotected 1- and 2-Naphthalenecarboxylic Acids. A Facile Route to 1,1,2- and -1,2,2-Trisubstituted 1,2-Dihydronaphthalenes

“…The conjugate addition reactions of α,β-unsaturated carboxylic acid derivatives can be promoted by steric interference with the 1,2-addition process. Organolithium reagents undergo predominantly 1,4-addition reactions with unsaturated trityl ketones , as well as amide acceptors derived from highly hindered amines …”