111349-77-0Relevant academic research and scientific papers
Catalytic enantioselective allyl- and crotylboration of aldehydes using chiral diol·SnCl4 complexes. Optimization, substrate scope and mechanistic investigations
Rauniyar, Vivek,Zhai, Huimin,Hall, Dennis G.
supporting information; scheme or table, p. 8481 - 8490 (2009/02/02)
We report a novel class of C2-symmetric chiral diols derived from the hydrobenzoin skeleton. The combination of these diols with SnCl 4 under Yamamoto's concept of Lewis acid assisted Bronsted acidity (LBA catalysis) leads to high levels of asymmetric induction in the allylboration of aldehydes by commercially available allylboronic acid pinacol ester 1a. The corresponding homoallylic alcohol products of synthetically useful aliphatic aldehydes are obtained in excellent yields with up to 98:2 er. This combined acid manifold is also efficient in catalyzing the diastereo- and enantioselective crotylboration of aldehydes, thus providing the propionate units in >95:5 dr and up to 98:2 er. The X-ray crystal structure of the optimal diol·SnCl4 complex, Vivol (4m)·SnCl 4, unambiguously shows the Bronsted acidic character of this LBA catalyst and its highly dissymmetrical environment. Further controls have ruled out a possible boron transesterification mechanism with the chiral diol and point to LBA catalyst-derived activation of the pinacol allylic boronates 1. Due to slow dissociation of the diol·SnCl4 complex, a small excess of diol is required in order to suppress a competing racemic cycle catalyzed by free SnCl4.
Synthesis of the 1,6,8-trioxadispiro[4.1.5.2]tetradec-11-ene ring system present in the spirolide family of shellfish toxins and its conversion into a 1,6,8-trioxadispiro[4.1.5.2]-tetradec-9-en-12-ol via base-induced rearrangement of an epoxide
Brimble, Margaret A.,Furkert, Daniel P.
, p. 3573 - 3583 (2007/10/03)
The synthesis of the 1,6,8-trioxadispiro[4.1.5.2]tetradec-11-enes 12 present in the shellfish toxins spirolides B 1 and D 2, is reported. The two spirocentres were constructed via iterative radical oxidative cyclization of hydroxyalkyl dihydropyran 14 and
Synthesis of the C10-C22 bis-spiroacetal domain of spirolides B and D via iterative oxidative radical cyclization.
Furkert, Daniel P,Brimble, Margaret A
, p. 3655 - 3658 (2007/10/03)
[reaction: see text] A synthetic approach to the novel bis-spiroacetal moiety of spirolides B and D is reported. The strategy hinges upon successive formation of the spirocenters at C15 and C18 by radical oxidative cyclization, followed by base-induced re
Synthesis of an oxaspirolactone intermediate for the synthesis of spirolides
Brimble, Margaret A.,Fares, Fares A.,Turner, Peter
, p. 845 - 851 (2007/10/03)
A new method has been established for the preparation of C2-oxidized 5,5-spiroacetals, which are key intermediates for the synthesis of the bis-spiroacetal moiety of the spirolides. A bridged orthoester was used as a masked carboxylic acid in the preparat
Allyltitanates in stereospecific additions to chiral σ-lactol: Efficient enantioselective route to a potential precursor of the C1-C9 portion of Tylonolide
Berque, Isabelle,Le Menez, Patrick,Razon, Patrick,Mahuteau, Jacqueline,Ferezou, Jean-Pierre,Pancrazi, Ange,Ardisson, Janick,Brion, Jean-Daniel
, p. 373 - 381 (2007/10/03)
The Hoppe reaction, which is an allylation reaction of aldehydes using an optically active titanated crotyl carbamate intermediate generated from the corresponding N,N-diisopropyl crotyl carbamate with n-BuLi/(-)-sparteine, was in most cases applied to achiral aldehydes. In this work an extension of this reaction is reported using a racemic γ-alkoxy allyltitanate (17) and an optically active aldehyde (16) to deliver in good yield the anti adduct 18 as the major isomer. When the corresponding σ-lactol 24 was used in place of aldehyde 16, the anti adduct 25 was obtained in 94% yield as the only product. Structural modifications effected on 25 delivered aldehyde 28 which was in turn submitted to a second allylation reaction in the presence of the optically active titanated crotyl carbamate 2, prepared as described by Hoppe from crotyl carbamate 1, to conduct to compound 29 in 80% yield. This derivative corresponds to a potential precursor of the C1-C9 portion of Tylonolide, aglycon of Tylosin (4).
Asymmetric synthesis of calyculin C. 1. Synthesis of the C1-C25 fragment
Scarlato, Gerard R.,DeMattei, John A.,Chong, Lee S.,Ogawa, Anthony K.,Lin, Mavis R.,Armstrong, Robert W.
, p. 6139 - 6152 (2007/10/03)
We report our synthesis of the C1-C25 fragment of serine/threonine phosphatase PP1 and PP2A inhibitor, calyculin C. Synthetic efforts were directed initially toward the synthesis of a spiroketal core fragment (7), which culminated in completion of the bottom half of the natural product. The synthesis of fragment 7 and subsequent elaboration relied on an allylboration strategy for introduction of chirality. The C1-C8 fragment representing the potentially unstable tetraene moiety was introduced as a separate entity.
The chemistry of cyclic vinyl ethers. 6. Total synthesis of polyether ionophore antibiotics of the calcimycin (A-23187) class
Boeckman Jr., Robert K.,Charette, André B.,Asberom, Theodros,Johnston, Brian H.
, p. 5337 - 5353 (2007/10/02)
An extremely convergent (longest linear sequence, 16 steps), fully stereoselective, and potentially general synthesis of the antibiotic ionophores of the Calcimycin (A-23187) class was devised. The key steps involve a coupling reaction between the chiral nonracemic subunits dihydropyran 41 (as the α-lithio anion) and bromide 49. Subsequent acid-promoted cyclization directly produces the spirocyclic ring system found in the ionophore X-14885A (3). Alternatively, cyclopropanation of substituted vinyl ether 55 followed by acid treatment afforded the spiroketal 58 that was subsequently converted into the polyether ionophore Calcimycin (1) and also Cezomycin (2).
