Ylide compounds intramolecular reactions

In contrast to considerations of 50 years ago, today carbene and nitrene chemistries are integral to synthetic design and applications. Always a unique methodology for the synthesis of cyclopropane and cyclopropene compounds, applications of carbene chemistry have been extended with notable success to insertion reactions, aromatic cycloaddition and substitution, and ylide generation and reactions. And metathesis is in the lexicon of everyone planning the synthesis of an organic compound. Intramolecular reactions now extend to ring sizes well beyond 20, and insertion reactions can be effectively and selectively implemented even for intermolecular processes. 

Whereas phosphonium ylides normally react with carbonyl compounds to give alkenes, dimethylsulfonium methylide and dimethylsulfoxonium methylide yield epoxides. Instead of a four-center elimination, the adducts from the sulfur ylides undergo intramolecular displacement of the sulfur substituent by oxygen. In this reaction, the sulfur substituent serves both to promote anion formation and as the leaving group. 

As with any modern review of the chemical Hterature, the subject discussed in this chapter touches upon topics that are the focus of related books and articles. For example, there is a well recognized tome on the 1,3-dipolar cycloaddition reaction that is an excellent introduction to the many varieties of this transformation [1]. More specific reviews involving the use of rhodium(II) in carbonyl ylide cycloadditions [2] and intramolecular 1,3-dipolar cycloaddition reactions have also appeared [3, 4]. The use of rhodium for the creation and reaction of carbenes as electrophilic species [5, 6], their use in intramolecular carbenoid reactions [7], and the formation of ylides via the reaction with heteroatoms have also been described [8]. Reviews of rhodium(II) ligand-based chemoselectivity [9], rhodium(11)-mediated macrocyclizations [10], and asymmetric rho-dium(II)-carbene transformations [11, 12] detail the multiple aspects of control and applications that make this such a powerful chemical transformation. In addition to these reviews, several books have appeared since around 1998 describing the catalytic reactions of diazo compounds [13], cycloaddition reactions in organic synthesis [14], and synthetic applications of the 1,3-dipolar cycloaddition [15]. 

The cyclic ylide intermediate 366, as a 1,3-dipole, is generated by intramolecular reaction of Rh-carbene with the ketone in 365, and undergoes cycloaddition with n-bonds to give the adduct 367 [121]. When a-diazocarbonyls have additional unsaturation, domino cyclizations occur to produce polycyclic compounds. The Rh-carbene method offers a powerful tool for the construction of complex polycyclic molecules in short steps, and has been applied to elegant syntheses of a number of complex natural products. 

There is a report describing intramolecular, stereoselective cyclopropanations by utilizing the ylide reaction Preparation of tricyclic compounds, such as 24, has been accomplished by intramolecular reaction of phosphorous ylide generated in situ by addition of enolate anion to vinylphosphonium salt (equation 82) . Optically active... 

Hofmann degradation usually occurs with -elimination (El reaction). Wittig and Polster85 86 discovered a variant in which quaternary ammonium compounds are converted by strong bases such as phenyl- or butyl-lithium into olefins, by way of ylides, with intramolecular cw-elimination 87... 

Fused ring systems have been synthesized using both inter- and intra-molecular Wittig reactions. Various polyaromatic compounds, e.g., (169), have been prepared in one step by the reaction of the diylide (168) with the appropriate o-quinone. An intramolecular reaction of ylide (170) has been used to synthesize the dihydronaphthacene (171) as an early step in the synthesis of 3-demethoxyaranciamycinone, an anthracyclinone analogue. ... 

Reactions with -Dicarbonyl Systems Formation of lodo-nium Ylides Intramolecular Cyclopropanation. -Dicarbo-nyl compounds upon reaction with PhI(OAc)2 and KOH/MeOH at 0 °C yield isolable iodonium ylides (eq 22). This is a general reaction which requires two stabilizing groups flanking the carbon of the C=I group, such as NO2 and S02Ph. Decomposition of unsaturated analogs in the presence of Copper(I) Chloride proceeds with intramolecular cyclopropanation (Table 1). ... 

Metal-carbenoid intermediates derived from diazo compoimds undergo a variety of useful reactions, including yUde formation, cyclopropanation and insertion. In recent years, several excellent reviews [1-19] and books [20-29] have appeared on various aspects of this chemistry. Several reviews on car-benoid chemistry have major sections on 1,3-dipolar cycloadditions of carbonyl ylides. Because of the historical central prominence of carbenoids derived from diazocarbonyl compounds, most reviews have tended to focus on these species. These carbenoids are capable of generating carbonyl ylide dipoles via inter- or intramolecular reactions (Fig. 1). 

In the absence of double bonds, intramolecular insertion reactions into C-H bonds are observed (eq 8).22 Recently, intramolecular insertion into the B-H bond of a carborane has been found to occur readily.Anhyd CUSO4 has also been used effectively to promote the formation of sulfur ylides in the reactions of diazo compounds and sulfides. See also copper(I) acetylacetonate. 

Later on, the same group developed another three-component reaction of diazo compounds with anilines and 4-oxo-enolates based on their previous work [44], By controlling the addition sequence of the substrates, this three-component reaction could proceed through an aza-Michael addition/ylide generation/intramolecular aldol... 

In 2008, Zhang et al. succeeded in a three-component cascade reaction using achiral Ru and chiral Zr catalysis [14]. Under the influence of achiral Rh(OAc)j, oxonium ylide was generated from diazo compound 37 and alcohol 38. Consequently, this reactive intermediate was trapped by aldehyde 39 through a Lewis acid-promoted enantioselective aldol-type addition, yielding the chiral building blocks 40 with high levels of stereocontrol (Scheme 9.11). It should be noted that the presence of acidic Zr catalyst can also suppress the undesired irreversible intramolecular proton transfer of the oxonium ylide to benefit reaction pathway control. 

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