Ylides cyclopropane synthesis

Reagent-controlled asymmetric cyclopropanation is relatively more difficult using sulfur ylides, although it has been done. It is more often accomplished using chiral aminosulfoxonium ylides. Finally, more complex sulfur ylides (e.g. 64) may result in more elaborate cyclopropane synthesis, as exemplified by the transformation 65 66 ... 

Miscellaneous Iminium Catalyzed Transformations The enantioselective construction of three-membered hetero- or carbocyclic ring systems is an important objective for practitioners of chemical synthesis in academic and industrial settings. To date, important advances have been made in the iminium activation realm, which enable asymmetric entry to a-formyl cyclopropanes and epoxides. In terms of cyclopropane synthesis, a new class of iminium catalyst has been introduced, providing the enantioselective stepwise [2 + 1] union of sulfonium ylides and ot,p-unsaturated aldehydes.As shown in Scheme 11.6a, the zwitterionic hydro-indoline-derived catalyst (19) enables both iminium geometry control and directed electrostatic activation of sulfonium ylides in proximity to the incipient iminium reaction partner. This combination of geometric and stereoelectronic effects has been proposed as being essential for enantio- and diastereocontrol in forming two of the three cyclopropyl bonds. 

The formation of the free carbene is also circumvented in certain cyclopropanation reactions involving sulfonium ylides. They readily react with electron-deficient alkenes in a Michael addition/ring-closure sequence (MIRC reaction). This cyclopropane synthesis will be dealt with separately in Section 1.1.3.7. 

Cyclopropane synthesis from electron-deficient alkenes and acylmethylenesulfonium ylides is discussed in detail in Section 1.1.2. The advantage over the use of a-diazocarbonyl compounds may be illustrated by the synthesis of bicyclo[3.1.0]hex-3-en-2-one 28. ... 

For the synthesis of cyclopropyl amino acids, Williams has used an oxazinone auxiliary (cf. Scheme 3.12) as an electrophilic component in a sulfur ylide cyclopropanation using Johnson s sulfoximines, as illustrated in Scheme 6.41 [148]. Surprisingly, the sulfur ylide approaches from the P face the authors speculate that there may be some sort of 7t-stacking between the phenyls on the oxazinone ring and the phenyl in the sulfoximine to account for this [149]. With Corey s [147] dimethylsulfonium methylide, the diastereoselectivity was only about 75%, but with Johnson s sulfoximines (used in racemic form), only one diastereomer could be detected for most substrates studied (with the exception of R = H, [149]). Dissolving metal reduction afforded moderate yields of the cyclopropyl amino acids. 

Condensatioii Reactions.—Little emphasis has been placed on the use of condensation reactions in cyclopropane synthesis during the past year. Dimethylsulphoxonium methylide has been used for cyclopropanation of the side-chain double bond in brassicasterol, a A steroidal diene, due to the failure of carbene and carbenoid additions. Michael addition of the ylide (136) to acrolein affords an isomeric mixture of cyclopropanes, whereas addition to acrylonitrile stereoselectively gives only one isomer, the identity of which has not been established. An analogous... 

The one-pot synthesis of dibenzoyl cyclopropanes with a cis trans stereoselectivity by Wittig olefination-sulfur ylide cyclopropanation sequence has been described. When 0 CS2CO3 was used as the base and CHjCN/water (8 2, v/v) as the solvent, the major product was the c -1,2-dibenzoyl cyclopropane. In contrast, when using DBU as the base and MeOH as the solvent, the major product was fra i-dibenzoyl cyclopropane. 

Sulfur ylides are usually used for cyclopropanation [27]. Recently, chiral cyclopropane synthesis has been actively investigated. Chiral S-ylide 19 serves as a chiral donor for... 

Pyridinium ylides containing a chiral auxiliary served as a good precursor for cyclopropane synthesis (Scheme 1.30). Ohkata and coworkers reported that a-pyridinium 8-phenyl-menthylamide 50 achieved asymmetric cyclopropanation to give cyclopropane in up to a 98 2 diastereomeric ratio [51]. Yamada s group devised chiral pyridinium salts 51, which underwent asymmetric cyclopropanation [52]. Kanomata s group used planner chiral pyridinium ylides 52 for successful asymmetric cyclopropanation [53]. 

Diazomalonic esters serve as intermediates for the synthesis of a wide variety of compounds including cyclopropanes, cyclo-propenes, cycloheptatrienes, sulfur ylides, lactones, and substituted malonates. ... 

A very convenient asymmetric synthesis of cyclopropane or epoxide systems developed by Johnson (184) is based on the use of chiral sulfur ylides as the agents that induce optical activity. Generally, this method consists of the asymmetric addition of a chiral sulfur ylide to the C=C or C=0 bond and subsequent cyclization of the addition product to form a chiral cyclopropane or epoxide system together with chiral sulfinamide. A wide range of chiral... 

Doyle, M.P. McKervey, M.A. Ye, T. Modern Catalytic Methods for Organic Synthesis with Diazo Compounds From Cyclopropanes 20 to Ylides Wiley New York, 1998. 21... 

M. P. Doyle, M. A. McKervey, and T. Ye, Modem Catalytic Methods for Organic Synthesis with Diazo Compounds—from Cyclopropanes to Ylides, Wiley, New York, 1998. 

Sulfur ylides are among the most interesting carbon nucleophiles and their synthetic importance has been recently reviewed.One especially interesting use of these ylides is their application to the synthesis of cyclopropane derivatives using unsaturated oxazolones. For example, stabilized sulfur yhdes react with unsaturated oxazolones 629 via a Michael reaction to give oxazolone spirocyclopropanes 630 as shown in Scheme 7.202 and Table 7.46 (Fig. 7.57), whereas the less stabilized sulfur ylides give ring-opened products 631 as the major compounds (Scheme 7.202). ... 

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. 

So what is left to be accomplished During the current decade one can expect further asymmetric applications and catalyst designs for metathesis reactions, a maturing of chiral catalyst development for cyclopropanation and insertion with increasing synthetic applications, and decreased reliance on traditional Fischer carbenes in synthesis. Major changes remain for ylide applications, especially those that can be enantioselective, in catalytic carbene chemistry, and advances in nitrene chemistry that are comparable to those achieved over the years in carbene chemistry are in their infancy. 

Chiral cyclopropanes. Carrie el al.b l have developed a highly enantioselective synthesis of cyclopropanes from the aldehyde 2, in which the butadiene group is protected as the iron tricarhonyl complex. The complex (2) is resolved by the method of Kelly and Van Rheenan (5, 289-290), and the two optical isomers arc then converted separately into a cyclopropanealdehyde (5a and 5b) as formulated. A sulfur ylide such as (CH3)2S=CHCOOCH3 can be used in place of diazomethane for cyclopropanation. Optical yields are > 90%,... 

Doyle MP, McKervey MA, Ye T (1998) In Modern catalytic methods for organic synthesis with diazo compounds from cyclopropanes to ylides. Wiley, New York... 

Reviews have featured epoxidation, cyclopropanation, aziridination, olefination, and rearrangement reactions of asymmetric ylides 66 non-phosphorus stabilized carbanions in alkene synthesis 67 phosphorus ylides and related compounds 68 the Wittig reaction 69,70 and [2,3]-Wittig rearrangement of a-phosphonylated sulfonium and ammonium ylides.71 Reactions of carbanions with electrophilic reagents, including alkylation and Wittig-Homer olefination reactions, have been discussed with reference to Hammett per correlations.72... 

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