Total synthesis of (.+-.)-N-methylmaysenine

Catalytic Asymmetric Hetero Diels–Alder Reactions of N‐Sulfinyl Dienophiles with Chiral Bis(oxazoline)copper(II) and ‐zinc(II) Triflates

“…General: Benzyl N-sulfinylcarbamate (1a) [9] and N-sulfinyl-4-toluenesulfonamide (1b) [2b] were prepared according to the literature procedure and stored in the freezer as solutions in dry CH 2 Cl 2 . (S,S)-2,2Ј-Isopropylidenebis(4-phenyl-2-oxazoline) (4a), [10] [S(S),SЈ(S)]-N,NЈ-(2,6-pyridinediyldimethylidyne)bis[p-toluenesulfinamide] (5b), [23] (S,S)-1,2-bis(S-methyl-S-phenylsulfonimidoyl)benzene (6), [21] (E)-1-phenyl-1,3-butadiene (9), [17] and (1E,3E)-1methyl-4-phenylbutadiene (10), [17,19] were prepared according to the literature procedure. Analytical data for endo-3, exo-3, [7d] cis-11, trans-11, cis-12, and trans-12 [7a] are described elsewhere.…”

“…A series of chiral Lewis acids have previously been screened as promoters for the asymmetric HDA test reaction of N-sulfinyl dienophiles 1a [9] and 1b [2b] with 1,3-cyclohexadiene (2) shown in Scheme 1. [7] The best results were obtained with stoichiometric amounts of 4a-Cu(OTf) 2 or 4a-Zn(OTf) 2 [10] (Figure 1), providing the endo adducts 3a (X = Cbz) or 3b (X = Ts) in good enantioselectivities (90-98 % ee), diastereoselectivities (Ͼ90 % de), and yields (63-85 %). [7a,7b] Attempts to perform the test reactions with catalytic amounts of the Lewis acids gave rather disappointing results.…”

“…[4a-Zn(OTf) 2 ]: [10] An oven-dried round-bottomed flask was charged with copper(II) triflate or zinc(II) triflate (0.025 mmol) under an argon atmosphere. To this mixture, dry CH 2 Cl 2 (2 mL) and a solution of the phenyl bis(oxazoline) ligand (4a, 0.5 , 52 µL, 0.026 mmol) in CH 2 Cl 2 were added, and the resulting suspension was stirred for 2 h, at which time, most of the solids had dissolved.…”

Synthesis of maytansinoids: synthesis of an intermediate from D-glucose for the construction of maytansine

“…Because of the extremely low isolation yields of maytansine and its congenors, multifaced synthetic approaches toward this complex macrolide have been carried out by a number of research groups in the past several years (2), and the successful synthesis of Nmethylmaysenine has recently been reported from two research groups (3). Earlier work in this laboratory on the model studies for the synthesis of maytansine led to the stereocontrolled preparation of the model lactone i and the simple conversion i to compound ii, a cyclic carbamate unit of maytansine (4).…”

The μ3‐(η3Cη2O) Bridge—A Novel Mode of Coordination in the Structural Chemistry of Carbonylmetal Compounds

“…In contrast to the carbohydrates generally employed so far (see references cited in Is]) inexpensive tartaric acid has only two types (C, axis!) of functional groups, whose number can be readily doubled [see (I), (2)]; moreover, a C4 unit can be incorporated with less effort into a greater number of target molecules than a C6 building block.…”