61342-56-1Relevant articles and documents
Synthesis of four stereoisomers of (S)-2-methylpent-3-yl 3,13-dimethylpentadecanoate, a sex pheromone of the bagworm moth clania variegate, using stereospecific inversion of secondary sulfonates as a key step
Taguri, Tomonori,Yamamoto, Masanobu,Fujii, Toru,Muraki, Yuta,Ando, Tetsu
, p. 6924 - 6933 (2013/11/06)
Females of some lepidopteran species produce novel sex pheromones with a methyl-branched structure, such as 2-methylpent-3-yl 3,13-dimethylpentadecanoate secreted by the bagworm moth Clania variegate. Recently, we have established a simple preparative method for the synthesis of methyl-branched building blocks by utilizing an SN2 reaction of chiral secondary tosylates derived from (S)- and (R)-propylene oxides. The usefulness of these building blocks was demonstrated by their application in the synthesis of all four stereoisomers of an acid moiety in the bagworm pheromone. The enantiomeric purities of all building blocks were confirmed by enantioselective HPLC analysis. We found that a secondary mesylate was superior to the corresponding tosylate because it avoided an elimination side reaction, and racemization in the SN2 reaction was not observed even at high temperature (150 °C). Finally, each optically active acid was esterified with (S)-2-methyl-3-pentanol, which was synthesized by a new route starting from (S)-valine. A simple route to methyl-branched building blocks has been developed by utilizing an S N2 reaction of chiral secondary sulfonates derived from (S)- and (R)-propylene oxides. The usefulness of these building blocks was demonstrated by the stereospecific synthesis of all four stereoisomers of a bagworm pheromone. Copyright
Chiral fluorinated α-sulfonyl carbanions: Enantioselective synthesis and electrophilic capture, racemization dynamics, and structure
Hellmann, Gunther,Hack, Achim,Thiemermann, Eric,Luche, Olaf,Raabe, Gerhard,Gais, Hans-Joachim
supporting information, p. 3869 - 3897 (2013/04/10)
Enantiomerically pure triflones R1CH(R2)SO 2CF3 have been synthesized starting from the corresponding chiral alcohols via thiols and trifluoromethylsulfanes. Key steps of the syntheses of the sulfanes are the photochemical trifluoromethylation of the thiols with CF3Hal (Hal=halide) or substitution of alkoxyphosphinediamines with CF3SSCF3. The deprotonation of RCH(Me)SO2CF3 (R=CH2Ph, iHex) with nBuLi with the formation of salts [RC(Me)-SO2CF3]Li and their electrophilic capture both occurred with high enantioselectivities. Displacement of the SO2CF3 group of (S)-MeOCH2C(Me)(CH 2Ph)SO2CF3 (95 % ee) by an ethyl group through the reaction with AlEt3 gave alkane MeOCH2C(Me)(CH 2Ph)Et of 96 % ee. Racemization of salts [R1C(R 2)SO2CF3]Li follows first-order kinetics and is mainly an enthalpic process with small negative activation entropy as revealed by polarimetry and dynamic NMR (DNMR) spectroscopy. This is in accordance with a Cα-S bond rotation as the rate-determining step. Lithium α-(S)-trifluoromethyl- and α-(S)-nonafluorobutylsulfonyl carbanion salts have a much higher racemization barrier than the corresponding α-(S)-tert-butylsulfonyl carbanion salts. Whereas [PhCH 2C(Me)SO2tBu]Li/DMPU (DMPU = dimethylpropylurea) has a half-life of racemization at -105 °C of 2.4 h, that of [PhCH 2C(Me)SO2CF3]Li at -78 °C is 30 d. DNMR spectroscopy of amides (PhCH2)2NSO2CF 3 and (PhCH2)N(Ph)SO2CF3 gave N-S rotational barriers that seem to be distinctly higher than those of nonfluorinated sulfonamides. NMR spectroscopy of [PhCH2C(Ph)SO 2R]M (M=Li, K, NBu4; R=CF3, tBu) shows for both salts a confinement of the negative charge mainly to the Cα atom and a significant benzylic stabilization that is weaker in the trifluoromethylsulfonyl carbanion. According to crystal structure analyses, the carbanions of salts {[PhCH2C(Ph)SO2CF3] Li×L}2 (L=2 THF, tetramethylethylenediamine (TMEDA)) and [PhCH2C(Ph)SO2CF3]NBu4 have the typical chiral Cα-S conformation of α-sulfonyl carbanions, planar Cα atoms, and short Cα-S bonds. Ab initio calculations of [MeC(Ph)SO2tBu]- and [MeC(Ph)SO2CF3]- showed for the fluorinated carbanion stronger nC→σ* S-CF 3 and n O→σ* S-CF 3 interactions and a weaker benzylic stabilization. According to natural bond orbital (NBO) calculations of [R 1C(R2)SO2R]- (R=tBu, CF3) the nC→σS-R interaction is much stronger for R=CF3. Ab initio calculations gave for [MeC(Ph)SO2tBu] Li×2 Me2O an O,Li,Cα contact ion pair (CIP) and for [MeC(Ph)SO2CF3]Li×2 Me2O an O,Li,O CIP. According to cryoscopy, [PhCH2C(Ph)SO2CF 3]Li, [iHexC(Me)SO2CF3]Li, and [PhCH 2C(Ph)SO2CF3]NBu4 predominantly form monomers in tetrahydrofuran (THF) at -108 °C. The NMR spectroscopic data of salts [R1(R2)SO2R3]Li (R 3=tBu, CF3) indicate that the dominating monomeric CIPs are devoid of Cα-Li bonds. Worth their salt: Chiral Li α-(S)-trifluoromethylsulfonyl carbanion salts with ≥98 % enantiomeric excess (ee) and high configurational stability are accessible through the reaction of chiral triflones (≥98 % ee) with RLi (see figure). Their electrophilic capture occurs with high enantioselectivity. Studies of the structure and dynamics of chiral Li α-(S)-trifluoromethylsulfonyl carbanion salts revealed monomeric contact ion pairs. Copyright
Enantioselective synthesis, configurational stability, and reactivity of lithium α-tert-butylsulfonyl carbanion salts
Scholz, Roland,Hellmann, Gunther,Rohs, Susanne,Oezdemir, Diana,Raabe, Gerhard,Vermeeren, Cornelia,Gais, Hans-Joachim
supporting information; experimental part, p. 4588 - 4616 (2010/10/21)
The reactions of enantiopure S-tert-butyl sulfones of the type R 1CH(R2)SO2tBu (≥99% ee) with lithiumorganyl compounds gave the corresponding chiral α-sulfonyl carbanion salts [R 1C(R2)SO2tBu]Li with ≥94% ee. The enantioselectivity of the deprotonation of the phenyl- but not dialkyl-substituted sulfones is strongly dependent on the nature of the lithiumorganyl. Because of this observation and the strong decrease in enantioselectivity in the presence of TMEDA and HMPA, we propose an intramolecular proton transfer following complexation of the sulfone by RLi. Racemization of [R1C(R2)-SO2tBu]Li follows first-order kinetics and seems to be mainly an enthalpic process with a small negative activation entropy, as revealed by polarimetric measurements at low temperatures. This is in accordance with Cα-S bond rotation as the rate-determining step. The salts [R1C(R2)SO 2tBu]Li have half-lives of racemization in the order of several hours at -105°C. The deuteriation of the salts at -105°C with CF 3CO2D proceeded with enantioselectivities of 94% ee, the magnitude of which was not significantly affected by the presence of TMEDA and HMPA. The salts also reacted with carbon-based electrophiles at low temperatures with high enantioselectivity. The conversion of R1CH(R 2)SO2tBu via [R1C(R2)SO 2tBu]Li to R1C(R2,E)SO2tBu, which involves the loss of stereogenicity at the α-stereogenic center and its reestablishment upon reaction of the chiral carbanion with electrophiles, occurred with high overall enantioselectivity. Electrophiles attack the anionic C atom of [R1C(R2)SO2tBu]Li with high selectivity on the side syn to the O atoms and anti to the tert-butyl group. The reactivity of the dialkyl-substituted salts [R1C(R 2)SO2tBu]Li (R1, R2 = alkyl) is significantly higher than that of the benzylic salts [RC(Ph)SO2tBu]Li (R = alkyl) and the HMPA-coordinated SIPs of [MeC(Ph)SO2- tBu]Li are significantly more reactive towards EtI than the corresponding O-Li contact ion pairs.
Asymmetric syntheses of both enantiomers of amphetamine hydrochloride via bakers' yeast reduction of phenylacetone
Shi, Xiao-Xin,Yao, Jian-Zhong,Kang, Li,Shen, Chun-Li,Yi, Fei
, p. 681 - 683 (2007/10/03)
Both enantiomers of amphetamine hydrochloride were stereospecifically synthesised based on bakers' yeast reduction of phenylacetone. A simple and efficient method for the chiral inversion of (S)-1-phenyl-2-propanol 3 to (R)-1-phenyl-2-propanol 8 has been discussed.
