Stereoselectivity nucleophilic

In the synthesis of carpamic acid (98), Mitsutaka and Ogawa have used 1,2-dihydropyridine as a starting material [80H(14)169]. Photooxygenation of dihydropyridine 8h afforded enr/o-peroxide 96. Subsequent stereoselective nucleophilic reaction of 96 with ethyl vinyl ether in the presence of tin chloride gave tetrahydropyridinol 97, which was then converted into carpamic acid (98) in six more steps. 

Jackson and coworkers have used a new approach to the synthesis of fi-hydtoxy-ct-amino acids using farylthio nitrooxiranes. c-Jsopropylideneglyceraldehyde is converted into the corresponding 1-arylthio-l-nitroalkene, which is a key material for stereoselective synthesis of fi,Y-dihydroxyamino acids fScheme 4.6. The key step is stereoselective nucleophilic epoxlda-donof the Tarylthio-Tnltroalkene. Sy)i and ruin epoxides are selecdvely obtained by appropriate choice of epoxidadon reagent." ... 

Addition of Ketene Acetals and Enoles In recent years, much attention has been given to the synthesis of optically active nitrogen-containing compounds, with the key step being the highly stereoselective nucleophilic addition of ketene silyl acetals to nitrones (Scheme 2.174). Similar to nitrone cyanations, in ketene silyl acetal reactions one observes an accelerating effect with thiourea derivatives (633). 

For reviews dealing with stereoselective nucleophilic addition reactions, see (a) Lombardo M, Trombini C. Synthesis 2000 759-774 ... 

By virtue of their high stereoselectivity, nucleophilic additions to cyclobutanone derivatives have been utilized to prepare the five-membered rings of prostaglandins with complete control of stereochemistry. This chemistry has been reviewed.65 The conversion of 3-emio-(tert-butyldimethylsiloxy)tricyclo[3.2.0.02,7]heptan-6-one (30) to 7-am7-(3-terf-butyldimethylsiloxy-oct-l-enyl)-5- ,wdy-( rt-butyldimethylsiloxy)bicyclo[2.2.1]heptan-2-one (31) in 88% yield provides a good example.66... 

No reactions of t with protic solvents have been reported however, its cyclic analogue 1,2-diphenylcyclobutene (7) reacts with the protic solvents methanol, acetic acid, and water, to yield adducts 85 and 86 (eq. 28). The proposed mechanism for the formation of 85 and 86 involves the formation of singlet exciplex followed by proton transfer to yield a cyclobutyl cation 87. Stereoselective nucleophilic capture of 87 by solvent from its less hindered side yields 85, while skeletal rearrangement of 87 yields the cyclopropylmethyl cation 88, which reacts with solvent to yield 86 ... 

For compounds such as 63, a more complex rearrangement replaces the decarbonyla-tion reaction [65]. This photoisomerization yields lactone 64 by a-cleavage at C-2, C-3 position (Norrish I) and hydrogen transfer from C-l to C-3 followed by a stereoselective nucleophilic attack at the carbonyl group by the terminal carbon of the electron-rich double bond and final ring closure (Scheme 34). 

A short review of the first 100 years of ketene chemistry covers haloketenes, Wolff (g) rearrangements, stereoselective nucleophilic attack, dimerization, cycloadditions, ketene-Claisen and -Cope reactions, bisketenes, and free radical processes.12 ... 

Addition and cyclization reactions of imines, catalysed by IS r0 ns led acids, have been reviewed, including examples in water solvent and enantioselective cases.65 Another review examines stereoselective nucleophilic additions to the C=N bond of aromatic azines (60 references).66 (g)... 

Tatsui G (1928) Synthesis of carboline derivatives. J Pharm Soc Jpn 48 453 159 Taylor MS, Jacobsen EN (2004) Highly enantioselective catalytic acyl-pictet-spengler reactions. J Am Chem Soc 126 10558-10559 Terada M, Uraguchi D, Sorimachi K, Shimizu H (2005) Process for production of optically active amines by stereoselective nucleophilic addition reaction of imines with C nucleophiles using chiral phosphoric acid derivative. PCT Int Appl WO 2005070875 2005-08-04... 

Further results on the highly stereoselective nucleophilic ring-opening of chiral y-sul tones 112 have appeared <07S1837> and the reactions of p-halo-a,p-unsaturated y-sultones 113 with nucleophiles have also been reported <07JOC6824>. 

Imines formed from dienal complexes not surprisingly undergo stereoselective nucleophilic additions. Particularly... 

E. Cyclopropane Ring-closure by Stereoselective Nucleophilic Displacement... 

Carchon, G, Chretien, F, Chapleur, Y, Stereoselective nucleophilic addition on sugar hemiacetal controlled by large-ring chelates, Carbohydr. Lett., 2, 17-22, 1996. 

Table 16 Stereoselective Nucleophilic Additions to Oxathianyl Alkoxy Ketones (66) ...

TiCl4 is used extensively as a Lewis acid in numerous organic transformations, forming adducts that mediate reactivity. Such reactions include Diels Alder, 54,355 hetero Diels Alder,356 cyclization of olefinic aldehydes,357 Flosomi Sakurai allylic coupling reactions,358 cyclopropanations,359 chal-cogen-Baylis Flillman,360 Mukaiyama Aldol reactions,36 363 reductions of ketones to alcohols 364 and stereoselective nucleophilic additions to aldehydes.365... 

A truncated Passerini reaction between various aldehydes or ketones and a-alkyl-a-isocyanoacetamides in toluene at 70 °C in the presence of LiBr afforded 2,4,5-trisubstituted oxazoles in satisfactory yields (38-98%). For instance, stereoselective nucleophilic addition of 110 to A,A-dibenzylphenylalanal 111 led predominantly to the awfi-adduct 112 (dr = 9 1) which was smoothly converted after acidic hydrolysis of the oxazole ring into the dipeptide 113, containing an a-hydroxy-P-amino acid (norstatine) component <04T4879>. 

Stereoselective Nucleophilic Additions to Acyclic Carbonyl Groups The stereochemistry of nucleophilic addition to acyclic aldehydes and ketones is influenced by nearby substituents. A particularly important case occurs when there is a stereogenic center adjacent to the carbonyl group. As a result of the adjacent substituent, two diastereomers can be formed, depending on the direction of the approach of the nucleophile. The stereoselectivity of addition can be predicted on the basis of a conformational model of the TS. The addition reaction has been studied with several kinds... 

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