Sugars cycloadditions, chiral auxiliaries

However, most asymmetric 1,3-dipolar cycloaddition reactions of nitrile oxides with alkenes are carried out without Lewis acids as catalysts using either chiral alkenes or chiral auxiliary compounds (with achiral alkenes). Diverse chiral alkenes are in use, such as camphor-derived chiral N-acryloylhydrazide (195), C2-symmetric l,3-diacryloyl-2,2-dimethyl-4,5-diphenylimidazolidine, chiral 3-acryloyl-2,2-dimethyl-4-phenyloxazolidine (196, 197), sugar-based ethenyl ethers (198), acrylic esters (199, 200), C-bonded vinyl-substituted sugar (201), chirally modified vinylboronic ester derived from D-( + )-mannitol (202), (l/ )-menthyl vinyl ether (203), chiral derivatives of vinylacetic acid (204), ( )-l-ethoxy-3-fluoroalkyl-3-hydroxy-4-(4-methylphenylsulfinyl)but-1 -enes (205), enantiopure Y-oxygenated-a,P-unsaturated phenyl sulfones (206), chiral (a-oxyallyl)silanes (207), and (S )-but-3-ene-1,2-diol derivatives (208). As a chiral auxiliary, diisopropyl (i ,i )-tartrate (209, 210) has been very popular. 

The highly stereoselective 1,3-dipolar cycloaddition of C-phenyl-iV-glycosylnitrones (336) and (679) to dimethyl maleate D14, with the sugar moiety acting as a chiral auxiliary, has been used in enantioselective syntheses of isoxazolidines (678) and (678 ent) (Scheme 2.292) (118). 

Synthesis of p-lactam antibiotics from sugars (either as chiral auxiliary or chiron), describing the general methodology developed in 1990s by Chmielewski and based on [2 + 2] cycloaddition of isothiocyanides to sugar olefins, was also comprehensively reviewed.5... 

The Kunz group used a variety of sugar derivatives as chiral auxiliaries for the [2+2] cycloadditions of ketenes and enol ethers, which produced eventually highly substituted cyclobutanol derivatives [73]. 

The oxazolinone 107, a new recoverable chiral auxiliary that gives a high level of asymmetric induction in model aldol reactions and Diels-Alder cycloadditions (in which the reactant is connected to the auxiliary by -acylation), has been synthesized from L-gulonic acid. The key step in its synthesis was the thermal intramolecular nitiene insertion shown in Scheme 21. The formation of oxazolinethiones on hydrolysis of isothiocyanato-sugar derivatives is covered in detail in Chapter 9, section 3.3. Base-catalysed reaction of StS-O-isopropylidene-D-xylofuranosylamine with P-isothiocyanato-alkanals led to tricyclic derivatives such as 108, considered as cyclonucleoside analogues. ... 

Tamura, O, Mita, N, Kusaka, N, Suzuki, H, Sakamoto, M, Intramolecular cycloaddition of a-allyloxycarbonylnitrone bearing a chiral sugar auxiliary a short-step synthesis of the A-terminal amino acid component of nikkomycin Bz, Tetrahedron Lett., 38, 428-432, 1997. 

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