Nitrone-olefin cycloadditions

Asymmetric bias generated by protected vicinal diol controller and its application to asymmetric nitrone-olefin cycloaddition reactions 98YGK86. 

The elegant, enantiospecific synthesis of biotin (1) by Hoffmann-La Roche1 is based on a strategy that takes advantage of the powerful intramolecular nitrone-olefin cycloaddition reaction. Our analysis begins with model studies in which the straightforward conversion of L-cysteine (2) into aldehyde 3 (see Scheme 1) constitutes... 

Intramolecular Silyl Nitronate-Olefin Cycloaddition (ISOC)... 

The Michael addition of allyl alcohols to nitroalkenes followed by intramolecular silyl nitronate olefin cycloaddition (Section 8.2) leads to functionalized tetrahydrofurans (Eq. 4.15).20... 

Nitro compounds, synthesis of, 12, 3 Nitrone-olefin cycloadditions, 36, 1 Nitrosation, 2, 6 7, 6 Nucleosides, synthesis of, 55, 1... 

In this case, the exojendo selection coincides with the ratio of cis and trans annulation of ring A (formed by the cycloaddition) and ring B (formed from the tether which connects the reactive sites in the starting material). By means of the intramolecular cycloaddition, the exojendo selection may be significantly improved in a predictable manner (Section 2.3.6.). The exojendo problem is characteristic of all types of cycloadditions and enc reactions for instance, nitrone-olefin cycloaddition. 

The [3 +2] Nitrone-Olefin Cycloaddition Reaction Pal N. Confalone, Edward M. Hula... 

A variant of the above method is the nitrone-olefin cycloaddition, exploited for the synthesis of shikimic acid [349] and for the synthesis of the carbocyclic nucleoside neplanocin [350]. RCM has been recently exploited in Ziegler s synthesis of cyclophellitol [351]. This synthesis encompasses a number of steps described throughout this chapter, including chain extensions at Cl, at C6 and branching by Michael addition followed by carbocyclization. 

The complex Cp2Ti(OTf)2 induces [3 + 2]-nitrone-olefin cycloaddition reactions by a concerted process. The reaction proceeds via the intermediate [Cp2Ti(nitrone)2]2+. The crystal structure of one of these adducts is reported. Asymmetric induction has been observed when the chiral [Pg.592]

The chiral catalyzes asymmetric [3 + 2]-nitrone-olefin cycloaddition reactions.1559... 

There is no comprehensive review on the chemistry of isoxazolidines except for the specific aspect of the nitrone-olefin cycloaddition (1964)14 and on the cycloaddition of nitronic esters with olefins (1969).13 This review will cover the chemistry of isoxazolidines in the literature up to May 1974. 

Generally, the inversion at nitrogen is rapid and invertomer pairs are not isolated. In a few rare cases, however, a high nitrogen inversion barrier renders the invertomers separable.31 This point will be discussed later in more detail. The kinetic aspects of the nitrone-olefin cycloaddition have been extensively investigated by Huisgen32 and by Boyle.33... 

Dihydrofuraldehydes were prepared by an intramolecular silyl nitronate olefin cycloaddition with subsequent acidic workup <94JOC3783>. 

Chanoclavine I, ( )-isochanoclavine I Stereoselective total synthesis by a nitrone-olefin/ cycloaddition [21]... 

Several of the anthracycline antibiotics are highly effective against a wide variety of tumours, but possess a toxicity that severely limits dosage. In consequence considerable efforts have been directed towards modification of structure, and in one case lowering of toxicity has been achieved by replacing the carbohydrate moiety L-daunosamine (115) by its C-4 epimer L-acosamine (116). A chiral synthesis of both these compounds has now been reported. The key step is an intramolecular nitrone-olefin cycloaddition [(112) -> (113) and (114) in a ratio of 82 18] in which the chiral side-chain exerts considerable asymmetric induction. The major isomer (113) could be converted to either (115) or (116) by conventional means. 

Based on the enantioselective Michael addition/ISOC (intramolecular silyl nitronate olefin cycloaddition)/lragmentation sequence previously developed by the group of Rodriguez [33a], Shao and coworkers proposed an extrapolation for the construction of spirooxindoles catalyzed by a bifunctional tertiary amine-thiourea catalyst XV between 4-allyl-substituted oxindoles 63 and nitrostyrenes 64 (Scheme 10.21) [33b]. After the addition of TMSCl and EtgN at -30 C, the Michael adduct underwent an ISCX3 to afford the spiro oxime derivatives 65 in very good yields (85-85%), and excellent diastereo (up to >30 1) and enantioselectivities (94-99% ee) after the treatment with TBAF. 

Application of the intramolecular nitrone-olefin cycloaddition to 3-0-allyl-o-glucose derivatives 49 and 50 and their D-allo isomers 51 and 52 furnished pyranoisoxazolidines 53 with varying degrees of diastereoselectivity. The main product obtained from 50 gave 54 on trimming of the side chain. ... 

Scheme 37.1 Synthesis of bi- and tricyclic oxazolidines through Michael addition/nitrone formation/intramolecular [3+2] nitrone-olefin cycloaddition cascade reactions (Fu = fliryl).

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