Acyclic reagents

Approach (control) Acyclic (reagent) Cyclic (substrate) Acyclic (substrate) Acyclic (reagent) Acyclic... 

Nakajima Suga Sugita Ichikawa Tetrahedron 1969, 25, 1807. For cases of almost complete inversion, with acyclic reagents, see Piccolo Spreafico Visentin Valoti J. Org. Chem. 1985, 50, 3945 Piccolo Azzena Melloni Delogu Valoti J. Org. Chem. 1991,56, 183. 

Show how you would synthesize the following compounds, starting with benzene or toluene and any necessary acyclic reagents. Assume para is the major product (and separable from ortho) in ortho, para mixtures. 

The analysis of the structure of these sub-targets suggested the utilization of multifunctional cyclopentene derivatives such as the bicyclic lactone 158 and enone 159 (Scheme 3.41) as the most plausible precursors for the preparation of 155 and 157, respectively. The latter preparations involved (i) the synthesis of the acyclic reagents with a certain set of functionalities and (ii) utilization of these reagents to introduce the required appendage to the cyclopentane core of 158 or 159, followed, when necessary, by a sequence of trivial transformations. 

Acyclic Reagents. The alkenylation protocol between styrene, ethyl acrylate, or acrylonitrile and a 5-bromo- and 5-iodopyrimidine leads to coupling products 275 (Scheme 98) [143] Methoxy-, methylthio-, and amino groups are tolerated. i A triflyloxy substituent may replace the iodo substituent. 1-Methyl- and l,3-dimethyluracil-5-yl triflate... 

The condensation of two acyclic reagents (with any preattached substituents), one to supply N C W fragment and the other to supply C C C fragment to form the resulting ring, is the most used procedure and is known accordingly as the principal synthesis of pyrimidines. The approach is important for the synthesis of C -F pyrimidine derivatives. 

Electron deficient carbon-carbon double bonds are resistant to attack by the electrophilic reagents of Section 5.05.4.2.2(t), and are usually converted to oxiranes by nucleophilic oxidants. The most widely used of these is the hydroperoxide ion (Scheme 79). Since epoxidation by hydroperoxide ion proceeds through an intermediate ct-carbonyl anion, the reaction of acyclic alkenes is not necessarily stereospecific (Scheme 80) (unlike the case of epoxidation with electrophilic agents (Section 5.05.4.2.2(f)) the stereochemical aspects of this and other epoxidations are reviewed at length in (B-73MI50500)). 

The formation of g-alkyl-a,g-unsaturated esters by reaction of lithium dialkylcuprates or Grignard reagents in the presence of copper(I) iodide, with g-phenylthio-, > g-acetoxy-g-chloro-, and g-phosphoryloxy-a,g-unsaturated esters has been reported. The principal advantage of the enol phosphate method is the ease and efficiency with which these compounds may be prepared from g-keto esters. A wide variety of cyclic and acyclic g-alkyl-a,g-unsaturated esters has been synthesized from the corresponding g-keto esters. However, the method is limited to primary dialkylcuprates. Acyclic g-keto esters afford (Zl-enol phosphates which undergo stereoselective substitution with lithium dialkylcuprates with predominant retention of stereochemistry (usually > 85-98i )). It is essential that the cuprate coupling reaction of the acyclic enol phosphates be carried out at lower temperatures (-47 to -9a°C) to achieve high stereoselectivity. When combined with they-... 

Coupling reactions and related fluoroalkylations with polytTuoioalkyl halides are induced by vanous reagents, among them metals such as copper and zinc, or by an electrochemical cell. More recently, examples of carbon-carbon bond forma tion by coupling of unsaturated fluorides have been reported Both acyclic and cyclic fluoroolefins of the type (Rp)2C=CFRp undergo reducUve dimerization on treatment with phosphines [42] (equation 33) The reaction shown in equation 33 IS also accompbshed electrocheimcally but less cleanly [43]... 

The salt K2[SN2] is an important reagent for the preparation of other sulfur diimide derivatives when MesSiNSNSiMes is not sufficiently reactive. For example, both acyclic and cyclic arsenic(Iir) compounds, Bu2AsNSNAs Bu2 and BuAs(NSN)2As Bu, respectively, have been obtained in this way." ... 

A different type of behaviour is observed with the chloro Lewis acid BCI3. With this reagent halogen exchange occurs to produce the acyclic cation [N(SC1)2] , as the [BCU] salt, rather than NSCf. " Thiazyl trichloride NSCI3 is predicted to be unstable with respect to NSCl -1-Cl2. ... 

The conversion of a 4-arylazo-5-oxazolone into a 1,2,4-triazole by reaction with a Grignard reagent is mentioned in Section II, B, 3. In HiTnilar fashion, the rearrangement of compound 30 to derivatives of 3-carboxy-l,5-diphenyl-lfl -l,2,4-triazoles (40) proceeds readily in the presence of strong nucleophiles [Eq. (26)]. This transformation undoubtedly occurs by ring opening and dehydrative cychzation, and, indeed, the acyclic amide and hydrazide 41 have been isolated. ... 

Intramolecular [3-1-2] cycloadditions, i.e., having the TMM moiety and the acceptor linked by a tether, have great synthetic utility in polycarbocycle construction. The construction of 5.5, 6.5, and 7.5 ring systems has been demonstrated with this methodology [21-25]. A number of efficient routes to acyclic precursors were developed (Scheme 2.11). The organometallic reagent (31), generated from 2-bro-mo-3-(trimethylsilyl)propene (32) [26], is a key component in the construction of... 

Organoboron reagents ate pariictdarly well suited for 1,4-additions of aryl and vinyl groups to enones. Hayasbi et al. developed a highly enantioselective RliQ)/ BlNAP-catalyzed 1,4-addilion of pbenylbotonic add lo cyclic and acyclic enones [24] fSclieme 7.5) and 1-alkenylpbospbonales [25]. 

Cyclic and acyclic silyl enol ethers can be nitrated with tetranitromethane to give ct-nitro ketones in 64-96% yield fEqs. 2.42 and 2.43. " The mechanism involves the electron transfer from the silyl enol ether to tetranitromethane. A fast homolydc conphng of the resultant cadon radical of silyl enol ether with NO leads tn ct-nitro ketones. Tetranitromethane is a neutral reagent it is commercially available or readdy prepared. " ... 

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