Intramolecular ring opening of the epoxide

An asymmetric route affording a low yield of 3-carboxysultam 281 (R = R = R = H) has been described (see Section 4.05.7.3). As intermediate, compound 429 is prepared through intramolecular ring opening of the epoxide 428 obtained by Sharpless asymmetric epoxidation of the corresponding alkene <2000JOC7690>. 

An interesting reaction for the synthesis of cyclopropanes makes use of a tungsten carbonyl compound as the electrophile <05JOC5852>. An initial conjugate addition of lithiated epoxide 101 onto tungsten carbonyl 102 leads to intermediate 103, which then does an intramolecular ring opening of the epoxide to provide cyclopropane 104. 

In situ epoxidation of allenyl alcohols [20], aldehydes [21], acids [22] and sulfonamides [23] followed by intramolecular ring opening of the intermediates was thoroughly investigated by Crandall and co-workers. They showed that products formed either from the allene oxide or the spirodioxide intermediate can be prepared selectively. Allenyl acids 56, for example, react first with DMDO on their more substituted double bond. When the concentration of the oxidant is low (DMDO is formed... 

The vinyl silane 247 was unmasked to the ketone 250 by epoxidation, subsequent ring opening of the epoxide with HF in pyridine and concurrent cleavage of the THP and TBS protecting group (Scheme 39). The Stork-Jung annulation was completed through the treatment of the diketone 250 with sodium methoxide to mediate the intramolecular aldol con-... 

As is shown in Scheme 1.2.28, our retrosynthehc analysis led us to the ketodiol 127, providing access to the target pheromone after intramolecular acetalization. It was planned to prepare the dihydroxyketone 127 by diastereoselective ring opening of the epoxide 128 with either enantiomerically pure 3-pentanone SAMP... 

A possible mechanism for the PEG6000(NBu3Br)2-catalyzed cycloaddition of C02 with epoxides is proposed as shown in Scheme 5.2. The proposed mechanism involves the activation of propylene oxide (PO) by the ammonium cation (step I), the ring opening of the epoxide via nucleophilic attack of bromine at the least-hindered carbon (step II), and the insertion of C02 into the N-O bond (step III). Subsequent cyclization via an intramolecular nucleophilic attack (step IV) leads to the propylene carbonate (PC) and the regeneration of the catalyst. 

One synthesis of benzofurans is based on cyclofragmentation. An appropriately substituted sulfone is used as a nucleophile in intramolecular ring opening of an epoxide. The resulting molecule loses a sulfinate and formaldehyde. By immobilization of the sulfinate on a resin this sequence can be used for the cleavage of benzofurans from solid supports [112] (Scheme 6.1.31). 

A range of indolo(triazolo)-l,4-diazepine derivatives 104 were obtained by a microwave-heated three-component reaction involving tandem N-alkylation of indole 101 with epichlorohydrin 102, ring-opening of the epoxide with azide 103, and intramolecular azide-alkyne 1,3-dipolar cycloaddition reactions (13BJO401). Fused triazolodiazepinones were obtained via azide-alkyne 1,3-dipolar cycloaddition followed by lactamization (13JHC430). 

The intramolecular nucleophihc ring opening of the epoxide 165 of the penteno-nitrile [260] is less academic, and gives the hydroxynitrile 166 (Reaction scheme 105). 

Another of the well-established methods for the synthesis of a-hydroxy spiroacetals is through the intramolecular ring opening of an epoxide (Scheme 64). 

Benedetti, E Berti, R Fabrissin, S. Gianferrara, T. Intramolecular ring opening of epoxides by bis-activated carbanions. The influence of ring size on reactivity and selectivity. J. Org. Chem. 1994, 59, 1518-1524. 

However, these have not been the only approaches to the synthesis of these ring systems. For example, Sasaki et al. were able to use an intramolecular nucleophilic ring opening of an epoxide with sodium dimsylate to form the oxepane ring as illustrated in the conversion of 34 to 35 <99JOC9399>. 

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