The unexpected formation of trans-β-lactams in the reaction of α-iminoesters (RNC(H)C(O)OR′) with diethylzinc. Crystal structure of trans -1-(N -t -butyl)-3-(N-t -butyl-N-ethylamino)-4- methoxycarbonylazetidin-2-one

Umpolung Chemo- and Regioselective Cascade Addition of Diethylzinc to α-Diketones Followed by Intramolecular Michael Reaction: Stereoselective Synthesis of Highly Substituted 1- Indanones

Herein we report an efficient stereoselective umpolung 1,2-addition of Et₂Zn onto α-diketones followed by intramolecular cascade Michael cyclization. This strategy effectively delivers a broad range of substituted 1-indanones in excellent yields in a chemo- and regioselective fashion. Additionally, we performed a variety of synthetic transformations on the 1-indanone products. Furthermore, a hitherto-unexplored asymmetric variant of this methodology that provides up to 94:6 er using an easily accessible cinchona alkaloid ligand has been addressed.

Stable and Persistent Acyclic Diaminocarbenes with Cycloalkyl Substituents and Their Transformation to β-Lactams by Uncatalysed Carbonylation with CO

Four new acyclic diaminocarbenes (ADACs), viz. [(cyclo-C_n H_2n-1 )₂ N]₂ C (n=5-7) and iPr₂ N-C-N(cyclo-C₆ H₁₁ )₂ , were synthesised by reacting the corresponding formamidinium hexafluorophosphates with NaN(SiMe₃ )₂ . Their nucleophilicities and electrophilicities were respectively judged from the ¹ J_CH values determined for the N₂ CH unit of the corresponding formamidinium cations and from the ⁷⁷ Se NMR chemical shifts of the selenourea derivatives obtained from the reaction of elemental selenium with the corresponding ADACs. An ambiphilic profile essentially identical to that of the "Alder carbene" (iPr₂ N)₂ C was found in each case. Similar to the latter carbene, the new ADACs undergo a well-defined thermal decomposition by β-fragmentation, affording an alkene and a formamidine. The stabilities of [(cyclo-C_n H_2n-1 )₂ N]₂ C depend strongly on the value of n, following the order 6>5>7, with the latter congener being too unstable for isolation. [(cyclo-C₆ H₁₁ )₂ N]₂ C shows no thermal decomposition at room temperature in solution and is thus significantly more stable than (iPr₂ N)₂ C. The stability of iPr₂ N-C-N(cyclo-C₆ H₁₁ )₂ is intermediate between that of (iPr₂ N)₂ C and [(cyclo-C₆ H₁₁ )₂ N]₂ C, its β-fragmentation selectively affording propene and iPrN=CH-N(cyclo-C₆ H₁₁ )₂ . [(cyclo-C_n H_2n-1 )₂ N]₂ C (n=5-7) react readily with CO under mild conditions, selectively affording trisubstituted spirocyclic β-lactam derivatives with an antimicrobial activity spectrum similar to that of penicillin G.

C- and N-Selective Grignard Addition Reactions of α-Aldimino Esters in the Presence or Absence of Zinc(II) Chloride: Synthetic Applications to Optically Active Azacycles

Highly practical synthetic methods were developed for the C- and N-selective Grignard addition reactions of N-4-MeOC6H4-protected α-aldimino esters in the presence or absence of zinc(II) chloride. Diastereoselective C-alkyl addition, tandem C-alkyl addition-N-alkylation, and some transformations to synthetically useful optically active azacycles were demonstrated.

Integrated reactions using addition to conjugated imines and iminium salts

Recently, nucleophilic addition reactions to imino functions have been utilized in many crucial steps for the synthesis of bioactive and functional materials. This article summarizes the integrated “umpolung” reactions of α-imino esters and the use of iminium salts as reactive electrophiles. Regarding the umpolung reactions, the following five reactions are discussed: (1) N-alkylation/homocoupling; (2) tandem N-ethylation/C-allylation; (3) tandem N-ethylation/C-cyanation; (4) reduction of imines with tris(trimethylsilyl)aluminum; and (5) N-alkylation and Claisen rearrangement. Moreover, the generation and reactions of alkoxycarbonyl iminium species are also discussed. These are prepared easily from trisubstituted amino ketene silyl acetals by oxidation, and the subsequent nucleophilic addition of various nucleophiles readily affords the addition products.

Conjugated imines and iminium salts as versatile acceptors of nucleophiles

Growing interests in nitrogen-containing molecules involving bioactive and functional materials have stimulated the recent development of synthetic methodologies where nucleophilic addition reactions to imino carbons are utilized in crucial steps. This article summarizes double nucleophilic addition reactions with alpha,beta-unsaturated aldimines, addition reactions using alkynyl imines, "umpoled" reactions of alpha-imino esters, and the use of iminium salts as reactive electrophiles.

Tandem N-alkylation-C-allylation reaction of alpha-imino esters with organoaluminums and allyltributyltin

On treatment of various alpha-imino esters with organoaluminum reagents and allyltributyltin in the presence of benzoyl peroxide, the tandem reaction proceeded to give the N-alkylation-C-allylation products in good yields. The tandem N-alkyation-C-cyanation also proceeded using silyl or aluminum cyanide to give the aminonitrile in good yield.