Silyl coupling partner

Pyrimidine was used as an effective directing group for the a-arylation of pyrroles in a reaction between pyrroles 62 and silyl coupling partner 63... 

With an effective strategy for construction of the diazofluorene established, we set out to prepare the coupling partners required for synthesis of (—)-kinamycin F (6). The synthesis of the enone 117 began with meta-cresol (128, Scheme 3.23). Silylation formed the silyl ether 119 in nearly quantitative yield. Birch reduction of the silyl ether 119 formed the cyclohexadiene derivative 129 in excellent yield. Asymmetric dihydroxylation [52] of 129 occurred regioselectively to afford the... 

Alkynes have also been employed as a third coupling partner to afford silylated aUyhc derivatives. 

Five steps were required to convert 75 into the iodide coupling partner 44 needed for union with dithiane 43 (Scheme 17.16). Thioacetal formation31 and concomitant deketalisation were instigated by reacting 75 with 1,3-propanedithiol under Lewis acid conditions. Triol 76 was isolated in 65% yield. The less-hindered primary hydroxyl of 76 was then selectively 0-tosylated, and the remaining hydroxyls masked as tert-butyldimethyl silyl (TBDMS) ethers. Iodide displacement on 77 with sodium iodide and copper bronze,32 and transketalisation with N-chlorosuccinimide (NCS)/silver nitrate33 finally secured 44. 

Silyl oxazoles 55 have been used as precursors to 4-halooxazoles 56, which can then serve as coupling partners in Pd-catalyzed Sonogashira coupling reactions <2000SL692>. The silylated oxazole 55 was prepared in good yield by a Huisgen oxazole synthesis which involved a rhodium-catalyzed reaction between ethyl (triethylsilyl)diazoacetate 54 and benzonitrile (Scheme 7). 

A number of techniques have been employed to alleviate this issue such as complexation of the electron pair on nitrogen of the heterocycle with a Lewis acid prior to C-H deprotonation, and the use of C-2 silyl-oxazoles which tend to react as a coupling partner via the ring-closed form. 

As outlined in Scheme 6, isovanillin (35) was converted to aryl iodide 36 via MOM-protection, protection of the aldehyde, and subsequent iodination. Hydrolysis of the acetal and Wittig olefination delivered phenol 37 after exposure of the intermediate aldehyde to methanolic hydrochloric acid. Epoxide 41, the coupling partner of phenol 37 in the key Tsuji-Trost-reaction, was synthesized from benzoic acid following a procedure developed by Fukuyama for the synthesis of strychnine [62]. Birch reduction of benzoic acid with subsequent isomerization of one double bond into conjugation was followed by esterification and bromohydrin formation (40). The ester was reduced and the bromohydrin was treated with base to provide the epoxide. Silylation concluded the preparation of epoxide 41, the coupling partner for iodide 37, and both fragments were reacted in the presence of palladium to attain iodide 38. 

A rhodium-catalyzed transannulation of tosyl-triazoles 9 with silyl or alkyl enol ethers 10 was developed that allows for the synthesis of substituted pyrroles 11 with regiocontrol.The addition ofTsOH promotes the final dehydration step to afford pyrroles with different functionality. The method can also be adjusted to allow for the synthesis of 3-pyrrolin-2-ones by using silyl ketene acetals as one of the coupling partners (14TL6455). 

A survey of coupling partners shows this to be a very general method that tolerates several functionaHties and proceeds readily at room temjjerature. Unlike most TBAF-promoted reactions, however, the Z-isomer of the silanol reacts at a much lower rate than the -isomer. In general, electron-deficient aryl iodides couple faster than their electron-rich counterparts. The synthetic potential of this new method of activation is clearly demonstrated in the synthesis of ( )-and (Z)-64. The coupHng reaction occurs cleanly in the presence of a TBS (t-butyldimethylsilyl)-protected alcohol, without any observable deprotection. Thus, not only is the compatibihty with silyl protective groups estabhshed, the concept of employing the silanol moiety as a prosthetic group for controlled carbon-carbon... 

This method was employed in the stereospecific construction of a silyl diene in a synthesis of chlorotri-cholide (Scheme 2.80). The boronic acid partner 2.233 was prepared by hydroboration and hydrolysis. The vinyl iodide was 2.235 prepared by hydroalumination-iodination. The silyl group was included in order to boost stereoselectivity in the later Diels-Alder reaction, but also served to facilitate the synthesis of the vinyl iodide coupling partner. The Suzuki coupling yielded the diene 2.236 with retention of the stereochemistry of both alkenes. Thallium hydroxide was employed as the Lewis base. Thallium-containing Lewis bases have been found to be advantageous in a number of cases, but the toxicity of thallium is a serious concern. 

Again, the coupling partners can contain functional groups ester, acetals, amides, olefins, silyl ethers, and alcohols. 

Similarly, a variety of aryl ethers can be obtained via the [4-1-2] cross-benzannulation reaction of enynes with diynes (Scheme 14.24) [18]. Notably, using this strategy, alkoxy substituent can be introduced at positions 2, 4, and 6 of ary-lacethylene 65 with the use of appropriate coupling partners. Moreover, starting from silyl ethers, the corresponding p-alkynylphenols can be synthesized after deprotection in either a stepwise or a one-pot fashion [18b],... 

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