Synthetic potential

Two efficient syntheses of strained cyclophanes indicate the synthetic potential of allyl or benzyl sulfide intermediates, in which the combined nucleophilicity and redox activity of the sulfur atom can be used. The dibenzylic sulfides from xylylene dihalides and -dithiols can be methylated with dimethoxycarbenium tetrafiuoroborate (H. Meerwein, 1960 R.F. Borch, 1968, 1969 from trimethyl orthoformate and BFj, 3 4). The sulfonium salts are deprotonated and rearrange to methyl sulfides (Stevens rearrangement). Repeated methylation and Hofmann elimination yields double bonds (R.H. Mitchell, 1974). 

The reaction is named after Georg Wittig a German chemist who shared the 1979 Nobel Prize in chemistry for demonstrating its synthetic potential... 

The synthetic potential of nitrenes is more readily apparent in the synthesis of ring-fused systems (81AHC(28)309), which can be accomplished by cyclization onto a heteroatom or onto an adjacent ring, the latter having the possibility of reaction at carbon or at a heteroatom. 

Since syntheses of three-membered rings with two heteroatoms almost always proceed under mild conditions with good yields and from simple starting materials, they are useful intermediates in synthesis. The easy formation of N—O and N—N bonds offers synthetic potentialities. Furthermore, the three-membered ring may serve as a protecting group during additional operations of substitution. 

Oxaziridines unsubstituted at nitrogen as well as some iV-acylated oxaziridines offer synthetic potentialities due to their ability to transfer their nitrogen function to nucleophiles (Section 5.08.3.1.4). The simplicity of preparation of some aziridines from alkenes and the Spiro oxaziridine (S2) equals the simplicity of epoxidation. Aziridine (299), for example, is obtained by simple heating of indene with (52) in toluene (74KGS1629). 

Kinetic studies have shown that the enolate and phosphorus nucleophiles all react at about the same rate. This suggests that the only step directly involving the nucleophile (step 2 of the propagation sequence) occurs at essentially the diffusion-controlled rate so that there is little selectivity among the individual nucleophiles. The synthetic potential of the reaction lies in the fact that other substituents which activate the halide to substitution are not required in this reaction, in contrast to aromatic nucleophilic substitution which proceeds by an addition-elimination mechanism (see Seetion 10.5). 

Trifluoromethyl-substituted diazonium betaines [176]. Synthetic routes to trifluoromethyl-substituted diazo alkanes, such as 2,2,2-trifluorodiazoethane [ 177, 7 78, 179] and alkyl 3,3,3-trifluoro-2-diazopropionates [24], have been developed Rhodium-catalyzed decomposition of 3,3,3-tnfluoro-2-diazopropionates offers a simple preparative route to highly reactive carbene complexes, which have an enormous synthetic potential [24] [3-1-2] Cycloaddition reactions were observed on reaction with nitnles to give 5-alkoxy-4-tnfluoromethyloxazoles [750] (equation 41)... 

Bis(tnfluoromethyl) substituted heterodienes, being the most reactive hetero-dienes known to date, must be regarded as having unique synthetic potential... 

One of the most actively investigated aspects of enamine chemistry has been the acylation process (i). Initial intensive studies by Hiinig (373-375) showed the ease of preparing a variety of 9-diketones and particularly the synthetic potential of acylated cyclic ketones as intermediates in the preparation of aliphatic keto acids, keto dicarboxylic acids and diketo dicarboxylic acids (376-378). 

The cation has considerable synthetic potential for a wide range of S/N compounds,... 

Haloacetyl groups have also a synthetic potential. Thus, pesticidal (alkylthio)-vinyl esters of phosphorus acid derivatives have been prepared by the introduction and subsequent displacement of two chlorine atoms in the acetyl moiety attached to the furazan ring (Scheme 69) [73GEP(0)2144393]. 

Appreciably higher is the synthetic potential of the methods based on the use of such precursors as (3-bromotellurenylvinylaldehydes 5 and (3-methyldibromotel-lurovinylaldehydes 6 [97DOK(357)504], By bubbling ammonia through a benzene solution of tellurenyl bromide 5,4,5-tetramethyleneisotellurazole Ig was prepared in 70% yield. 

Organozinc copper reagents have very broad synthetic potential and a number of typical expetimenlal procedures have recently been puhliidaed [99,100],... 

Highly strained cyclic compounds are accessible by an intramolecular variant. An instructive example for the synthetic potential of the McMurry coupling reaction is the synthesis of 3,3-dimethyl-1,2-diphenylcyclopropene 8 ... 

Although the Paterno-Buchi reaction is of high synthetic potential, its use in organic synthesis is still not far developed. In recent years some promising applications in the synthesis of natural products have been reported. The scarce application in synthesis may be due to the non-selective formation of isomeric products that can be difficult to separate—e.g. 6 and 7—as well as to the formation of products by competitive side-reactions such as Norrish type-I- and type-II fragmentations. 

An example for the synthetic potential is the formation of a fenestrane skeleton 11 from the open-chain compound 10 by a cascade of two consecutive intramolecular Pauson-Khand reactions, the yield in this case is however only 9% J... 

The pinacol rearrangement reaction is of limited synthetic importance although it can be a useful alternative to the standard methods for synthesis of aldehydes and ketones." Especially in the synthesis of ketones with special substitution pattern—e.g. a spiro ketone like 5—the pinacol rearrangement demonstrates its synthetic potential ... 

The important biological role of the isobacteriochlorins has decisively influenced the development of synthetic approaches leading to the isobacteriochlorin class of compounds. All of the naturally occurring isobacteriochlorins contain geminally dialkylated structural parts in the saturated pyrrole rings, which require special approaches for their synthesis. Until the discovery of siroheme and sirohydrochlorin, this structural element could only be found in vitamin B,2. Using the synthetic potential, which was invented during numerous syntheses of... 

Metalated epoxides can react with organometallics to give olefins after elimination of dimetal oxide, a process often referred to as reductive alkylation (Path B, Scheme 5.2). Crandall and Lin first described this reaction in their seminal paper in 1967 treatment of tert-butyloxirane 106 with 3 equiv. of tert-butyllithium, for example, gave trans-di-tert-butylethylene 110 in 64% yield (Scheme 5.23), Stating that this reaction should have some synthetic potential , [36] they proposed a reaction pathway in which tert-butyllithium reacted with a-lithiooxycarbene 108 to generate dianion 109 and thence olefin 110 upon elimination of dilithium oxide. The epoxide has, in effect, acted as a vinyl cation equivalent. 

In spite of their intrinsic synthetic potential, addition reactions of metal enolates of non-stabilized esters, amides, and ketones to epoxides are not widely used in the synthesis of complex molecules. Following the seminal work of Danishefsky [64], who introduced the use of Et2AlCl as an efficient catalyst for the reaction, Taylor obtained valuable spiro lactones through the addition reaction of the lithium eno-late of tert-butyl acetate to spiro-epoxides, upon treatment of the corresponding y-... 

These examples demonstrate that the synthetic potential of diazocyanides is broad and not yet exhaustively explored. It seems worthwhile to study these compounds in more detail ... 

The synthetic potential of such transformations for the preparation of medium-size heterocycles172 has been discussed elsewhere2. It is generally accepted that the reaction between thiirene dioxides and enamines is a stepwise (nonconcerted) thermal [2 -I- 2] cycloaddition. However, a concerted [4 + 2] cycloaddition, in which the lone pair of the enamine nitrogen atom participates, cannot be excluded. 

Fig. 6 RCM-based formation and synthetic potential of dihydropyrans VIII and a-pyrones II...

Fallis A. G., Lu Y. F. TT-Facial Diastereoselection in Diels-Alder Cycloadditions and Related Reactions Understanding Planar Interactions and Establishing Synthetic Potential Adv. Cydoaddit. 1993 3 1-66... 

The first chapter presents the general aspects of the reaction Chapters 2-6 illustrate the various methods and their applications in organic synthesis. At the end of each chapter a list of graphically abstracted Diels-Alder reactions is presented to show selected synthetic applications of the specific methodology. The discussion of the various topics is not exhaustive because our aim has been to emphasize the synthetic potential of each method. Chapter 7 reports a list of books, reviews, monographs and symposia proceedings which have appeared since 1990 and an index of keywords to help the reader find a particular paper of interest. 

In the following text, a brief overview of functionalization of various olefins is provided to give an outline of the current synthetic potential of this biooxygenation. 

The beauty of bromide-mediated oxidations is that they combine mechanistic complexity with practical simplicity and, hence, utility. They involve an intricate array of electron transfer steps in which bromine atoms function as go-betweens in transfering the oxidizing power of peroxidic intermediates, via redox metal ions, to the substrate. Because the finer mechanistic details of these elegant processes have often not been fully appreciated we feel that their full synthetic potential has not yet been realized. Hence, we envision further practical applications in the future. 

Zimmermann SC, Lawless LJ (2001) Supramolecular Chemistry of Dendrimers. 217 95-120 Zwanenburg B, ten Holte P (2001) The Synthetic Potential of Three-Membered Ring Aza-Heterocycles. 216 93-124... 

The Homer - Emmons reagent (52) is effective in the one carbon homologation of ketones possessing acidic a-hydrogen atoms <96SL875> and electron-deficient alkenes add to 2-phenylseleno-l,3-dithiane in a photo-initiated heteroatom stabilised radical atom transfer process, giving products of considerable synthetic potential <96TL2743>. 

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