149832-54-2Relevant academic research and scientific papers
PEPTIDE TURN MIMETICS
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Page/Page column 20, (2011/04/14)
Peptide mimetics of structure X herein which (i) provide a wide range of sidechain functions at all sidechain positions, (ii) can be incorporated in a peptide sequence, (iii) can be readily synthesized and (iv) have a variety of conformations. There is also provided a novel process which can provide valuable intermediates in relation to production of peptide mimetics of structure X which intermediates have a high degree of chemo- and stereo-selectivity. Preferred mimetics include structures I, II, III, IV, V and VI.
Asymmetric sulfur ylide reactions with boranes: Scope and limitations, mechanism and understanding
Fang, Guang Y.,Wallner, Olov A.,Di Blasio, Nadia,Ginesta, Xavier,Harvey, Jeremy N.,Aggarwal, Varinder K.
, p. 14632 - 14639 (2008/09/17)
The reactions of aryl-stabilized sulfur ylides with organoboranes has been studied under a variety of conditions. At 5 or -78°C, the reaction with Et3B gave a mixture of the first and second homologation products, but at -100°C, only the first homologation product was obtained even with just 1.1 equiv of Et3B. Under these optimized conditions, the chiral sulfur ylides (derived from camphor sulfonic acid) with different aryl groups were reacted with Et3B to give the corresponding alcohols (95-98% yield, 96-98% ee) and amines (74-77% yield, >98% ee). The origin of the high enantioselectivity is discussed. The use of nonsymmetrical 9-BBN derivatives was also explored. It was found that whereas primary alkyl substituents gave mixtures of products derived from competing migration of the boron substituent and the boracycle, all other groups resulted in either exclusive migration of the boron substituent (Ph, hexenyl, i-Pr) or exclusive migration of the boracycle (hexynyl, cyclopropyl). The factors responsible for the outcome of the reactions involving a hindered (i-Pr) and an unhindered (propynyl) substituent were studied by DFT calculations. This revealed that, in the case of an unhindered substituent, the conformation of the ate complex is the dominant factor whereas, in the case of a hindered substituent, the barriers to interconversion between the conformers of the ate complex and subsequent migration control the outcome of the reaction.
Radical allylation, vinylation, alkynylation, and phenylation reactions of α-halo carbonyl compounds with organoboron, organogallium, and organoindium reagents
Takami, Kazuaki,Usugi, Shin-Ichi,Yorimitsu, Hideki,Oshima, Koichiro
, p. 824 - 839 (2007/10/03)
Allylic gallium and indium reagents are found to mediate radical allylation reactions of α-iodo or α-bromo carbonyl compounds. Treatment of benzyl bromoacetate with allylgallium, prepared from allylmagnesium chloride and gallium trichloride, in the presence of triethylborane provided benzyl 4-pentenoate in excellent yield. Addition of water as a co-solvent improved the yields of allylated products. Allylic indium reagents are also useful and can replace the gallium reagents. A diallylborane reagent can allylate an α-iodo ester in good yield. Alkenylation reactions of α-halo carbonyl compounds with alkenylindium proceeded via a radical process in the presence of triethylborane. Unactivated alkene moieties and styryl groups were introduced by this method. The carbon-carbon double bond geometry of the alkenylindiums was retained during the alkenylation. Preparation of an alkenylindium via a hydroindation of 1-alkyne and subsequent radical alkenylation established an efficient one-pot strategy. Radical alkynylations and phenylations with organoindium reagents are disclosed herein.
A versatile synthesis of 9-BBN derivatives from organometallic reagents and 9-(triisopropylsilyl)thio-9-borabicyclo[3.3.1]nonane
Soderquist, John A.,Justo De Pomar, Jorge C.
, p. 3537 - 3539 (2007/10/03)
Representative B-substituted-9-BBNs (3) are efficiently prepared from either organolithium or Grignard reagents through their addition to (TIPS)S- 9-BBN (1) which is readily available from TIPSSH and 9-BBN-H. The thermally induced collapse of the intermediate 'ate' complexes (2) produces 3 which is easily isolated in good yield and high purity. (C) 2000 Elsevier Science Ltd.
Trans-vinylboranes from 9-borabicyclo[3.3.1]nonane through dehydroborylation
Colberg, Juan C.,Rane, Anil,Vaquer, Jaime,Soderquist, John A.
, p. 6065 - 6071 (2007/10/02)
The hydroboration of 1-alkynes (1) was reinvestigated by 11B NMR under optimized conditions (THF, 18 h, 0°C) and found to provide trans-vinyl-9-BBN adducts (2) together with variable amounts of 1,1-diborylalkanes (3) depending both upon the excess of 1 employed and the nature of alkyne substitution. By contrast, the formation of 3 with 2 equiv of 9-BBN-H is quantitative. A new completely stereoselective route to 2 from 3 was discovered with its reaction with ArCHO in an electrocyclic process (p = 0.42). While analogous to the Midland reduction, the term dehydroborylation is introduced to emphasize the olefination aspect of the reaction. Compound 3a (R = Me) is smoothly dehydroborylated at 25°C with PhCHO following second-order kinetics. Competitive rate studies reveal its reaction to be slower than that of Alpineborane (7) (k7/k3a = 4.5) but faster than that of B-siamyl-9-BBN (6) (k6/k3a = 0.34). The value of the dehydroborylation approach to 2 and the advantages of using 9-BBN derivatives in vinylborane reactions are demonstrated with numerous examples. Thus, 1,8-nonadiyne is converted, through a bis(vinylborane) (11), to pure trans,trans-1,9-dideuterio-1,8-nonadiene (12). This transformation has not been previously possible for 9-BBN-H because of competitive dihydroboration. The dihydroboration of 1-(triethylsilyl)-1-propyne, after thermal isomerization and deuterolysis, affords trans-(3-deuterioallyl)silane (16), a most remarkable overall conversion. The insertion of aromatic aldehydes into 2 was further demonstrated to provide a convenient entry to trans-allylic alcohols. The selective oxidation of 2 with TMANO produces trans-alkenyl-9-oxa-10-borabicyclo[3.3.2]decanes, 18, which resist further reaction with ArCHO, oxidation in the atmosphere, and protonolysis. A 1→ 3 → 2 → 20 sequence was employed without the isolation of 2 in a one-pot Suzuki coupling with ArBr to provide trans-stilbenes (20, Ar = p-C6H4X, X = OMe (80%), NMe2 (60%)).
