Spiro-oxazolidinones

Padwa has shown that rhodium-catalyzed oxidation of indolyl carbamate 67 employing either Phl(OAc)2 or Phl=0 follows a path similar to that of the D-aUal carbamate (Scheme 17.26) [95]. In principle, indole attack of the putative rhodium-nitrene generates zwitterion 68, which is trapped subsequently by an exogenous nucleophile. Spiro-oxazolidinone products (for example, 69) are isolated as single diastereomers in yields ranging from 50 to 85%. As an intriguing aside, Padwa has found that certain carbamates react with Phl=0 in the absence of any metal catalyst to furnish oxazoHdinone products. This result may have implications for the mechanism of the rhodium-catalyzed process, although it should be noted that control experiments by Espino and Du Bois confirm the essential role of the metal catalyst for C-H amination [57]. 

Ephedrine and tosylallene combine to form the oxazolidine (526) in a stereospecific addition/ The action of ketens R R C=C=0 on the fluoren-ylidenenitrones (527) may result in spiro-oxazolidinones (528) or the spiro-isoxazolidinones (529), depending on the nature of the groups R to... 

A number of interesting A-ring-fused heterocycles have been synthesized from steroidaI-2,3-aziridines including thiazolines and imidazo[2,l-6]thiazo-lines, and a typical synthesis of the latter type from (280) is outlined in Scheme J2 225 spontaneous elimination of HCl from the intermediate (281) is noteworthy since the equivalent regioisomeric intermediate obtained from the 2a,3 -epimers of (280) is quite stable. A number of 17-spiro-oxazolidinones... 

The three-component reaction between isatin 432a, a-aminoacids 433 (proline and thioproline) and dipolarophiles in methanol/water medium was carried out by heating at 90 °C to afford the pyrrolidine-2-spiro-3 -(2-oxindoles) 51. The first step of the reaction is the formation of oxazlidinones 448. Loss of carbon dioxide from oxazolidinone proceeds via a stereospecific 1,3-cycloreversion to produce the formation of oxazolidinones almost exclusively with /razw-stereoselectivity. This /f-azomethine ylide undergo 1,3-dipolar cycloaddition with dipolarophiles to yield the pyrrohdinc-2-r/ V -3-(2-oxindolcs) 51. (Scheme 101) <2004EJ0413>. 

N-Tosyl- and N-benzoyl-4-vinylidene-2-oxazolidinones underwent [4 + 2]-cycloaddi-tions with MVK at the enamide double bond to furnish the spiro adducts [154]. 

The alcohol 177 was converted to starting substrates oxazolidinone 178 by acylation followed by reduction of the azide function along with cyclization. Oxazolidinone 178 was protected with f-butylpyrocarbonate-4-(dimethylamino) pyridine (DMAP) and triethylamine, which was further subjected to reductive cleavage of the benzyl ester unit to afford carboxylic acid 179. The treatment of 179 with solution of l-chloro-/V./V,2-trimethyl-1-propenv I airline resulted in the easy formation of the corresponding acid chloride which on reaction with imine in the presence of triethylamine provided the stereoselective formation of spiro-p-lactam 180. 

Enantiomerically pure spiro oxindoles (Scheme 35) were prepared by using solid-supported N-cinnamoyl Evans oxazolidinone (164) [265]. Thus, chiral oxazolidi-none prepared from L-tyrosine was attached to a Merrifield resin and then N-acylated with the required unsaturated acyl chloride such as cinnamoyl chloride (not shown). The resin (165) was then suspended in aqueous dioxane and treated with proline and N-phenyl isatin at 80-90 °C overnight to give a highly substituted spiro compound (167). 

The substrate scope was expanded to cis-olefins and certain terminal olefins when a new series of glucose-derived ketones 4 and 5 were developed. In 2000, Shi reported an A -Boc oxazolidinone-bearing ketone 4 to be a highly enantioselective catalyst for the epoxidation of various cis-olefins conjugated with an aromatic or alkyne group. The stereopreference of the olefin appears to be directed by an attraction fi om the oxazolidinone moiety of ketone 4. In the transition state, Rrt substituent on the substrate prefers to be proximal to the oxazolidinone of ketone 4 (spiro C favored over spiro D). ... 

A Study on the epoxidation of non-conjugated cis-oleflns with oxazolidinone catalyst 13 has shown that hydrophobic and electronic interactions between the substituent and the catalyst can have a significant role in the selectivity of the reaction (Scheme 19.5) [46]. cis-AIkenes containing two substituents with very different hydrophobic/electronic properties can provide good systems for asymmetric epoxidation as they further reinforce preference for the favored spiro transition state seen above in Figure 19.5. 

The use of the Simmons-Smith reaction of allenes provides an efficient synthesis of novel spiro cyclopropanes. The use of chiral oxazolidinone-attached allenes 89 afforded chiral spiro[2.2]pentanes 90 and 91 (Scheme 1.48) [82]. 

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