TMS-amine initiators

R Glu = -(CH2)2COOCH2CeH5 Lys = -(CH2)4NHC(0)0CH2C6Hs Scheme 15 Polypeptide synthesis using TMS-amine initiators... 

The polymerizations initiated by HMDS and N-TMS amines usually complete within 24 h at ambient temperature with quantitative monomer consumption. These polymerizations in general are slower than those mediated by Deming s Ni(0) or Co (0) initiators (about 30-60 min at ambient temperature) [19, 24, 25], but are much faster than those initiated by amines at low temperature or using amine hydrochloride initiators [20]. These HMDS and N-TMS amine-mediated NCA polymerizations can also be applied to the preparation of block copolypeptides of defined sequence and composition [22]. This organosilicon-mediated NCA polymerization, which was also shown by Zhang and coworkers to be useful for controlled polymerization of y-3-chloropropanyl-L-Glu NCA [43], offers an advantage for the preparation of polypeptides with defined C-terminal end-groups. 

Another methodology is the deoxygenation of nitroxides by (TMSlsSiH, shown in Reaction (22). Indeed, the reaction of this silane with TEMPO, in the presence of thermal or photochemical radical initiators, afforded the corresponding amine in quantitative yield, together with the siloxane (TMS)2Si (H)OTMS. 

Fig. 1.7. Chromatogram of (A) initial amines 1 and 2 (see text) and (B) their TMS derivatives. From ref. 53.

Acylation is the most common method as amides are preferred over other kinds of derivatives. Their basicity is significantly less than that of amines and, hence, the pH of samples indicates that the influence is not as strong as on initial amines. Schiff bases and especially iV-trimethyl-silyl (TMS) derivatives are sensitive to postreaction hydrolysis. 

Some Alder-Ene products remain quite reactive therefore, trapping of the initial product may be required. Alder-Ene reactions of SO2 have been reported with subsequent trapping of the sulfinate ester with an amine to provide sulfonamides. In this case, the TMS group serves as the transferring group, but 83 was not suitable for isolation, and the amide 84 was prepared in good yield for this Conia-type Alder-Ene reaction. ... 

Since no reaction occurred at all in the absence of either the aldehyde catalyst or the base or both of them, as well as other proofs such as control reactions using high purity bases (>99.99 % purity), the authors concluded that the reaction is a true TM-free transformation. In addition to the aldehydes catalytic effect, the authors proved that imine intermediates and other TM-free oxidants could also be employed to initiate the reaction, which is consistent with, and further supports, the TM-free N-aUcylation mechanism (Scheme 39). Along with other results of mechanistic studies, the authors proposed a mechanism for the aldehyde-catalyzed A -alkylation reaction (Scheme 41). Firstly, the external aldehydes condense with amines/amides to give imine intermediates, which were then reduced by alcohols via a TM-free MPV-0 transfer hydrogenation process to give product amines and regenerate byproduct aldehydes as the new alkyl source in next reaction cycle. In the key TM-ffee transfer... 

After discovering the catalytic activity of aldehydes, Xu and co-workers later extended the method to TM-free aldehyde-catalyzed C-alkylation of secondary alcohols with primary alcohols [199] and catalyst-free C-alkylation reactions of methyl ketones with alcohols [200]. In 2013, Wu and co-workers also reported a closely related TM-free ketone-initiated C-alkylation of indole and pyrrole with secondary alcohols [201]. Similarly, Shi and co-workers employed conjugated ketones to catalyze the TM-free A/-alkylation reaction of amines with alcohols in 2015 (Scheme 42) [202], which is mainly suitable for benzylic and heterobenzylic alcohols, and anilines and heteroarylamines. Different ketones showed variant activities in the reaction (the catalysts were added in the same amount of 50 mg regardless of their molecular weights). In mechanistic studies such as the control reactions of the ketone catalyst and the substrate alcohol, up to 92 % ratio of the corresponding alcohol derived from reduction of the ketone catalyst can be detected in addition to formation of aldehdye intermediates derived from substrate alcohol. 

In 2013, Adimurthy and co-workers reported a TM-free NaOH-catalyzed N-alkylation reaction of 2-aminothiazoles, 2-aminobenzothiazoles, aminopyrimidines, and aminopyridines with benzyhc and heterobenzyhc alcohols under air (Scheme 43) [203]. In condition optimization, the authors found the model reaction of 2-aminobenzothiazole and 4-chlorobenzylalcohol under air afforded a higher yield of the product (93 %) than the one under nitrogen (90 %). Therefore, along with other results of mechanistic studies and the authors own previous work on based-catalyzed imine synthesis from alcohols and amines [204], they proposed that alcohol oxidation to aldehyde by air in the presence of bases is the initiation step of... 

In 2016, Xu and coworker reported another TM-fee aerobic Al-alkylation method for anilines, some heteroarylamines, and sulfinamides with alcohols (Scheme 49) [209]. As described in their work, these amines are not effective substrates under anaerobic catalyst-free autocatalyzed conditions, so an oxidant has to be employed to initiate the reaction. Differing from Yao and Zhao s protocol by adding O2 to an argon atmosphere [208], they found that a catalytic amount of air is active enough to initiate the reaction. In addition to primary alcohols, secondary alcohols can also be used as the aUcyl source. In mechanistic studies, the authors observed that primary and secondary alcohols underwent different initiation processes, i.e., primary alcohols require the presence of the amine to facilitate the aerobic oxidation to... 

Wirth recently demonstrated that an intramolecular reaction could indeed be realized with suitable induction, when a suitable chiral iodine(III) reagent was initially treated with TMS triflate followed by reaction at low temperature (Scheme 15) [54]. Conceptually, this process appears to be different from the usual pathways that originate from electrophilic nitrogen. Instead, the chiral hypervalent Ishihara reagent 70 probably leads to activation of one of the enantiotopic faces of the alkene 69 followed by nucleophilic amination and subsequent reductive de-iodination by oxygenation to arrive at the cyclic aminooxygenation product 71. 

Examples of additives are the following EA = iodonium salt, e.g. diphenyliodonium hexafluorophosphate (more rarely, a sulfonium salt) and related derivatives [113], alkyl halide, e.g. phenacyl bromide [1.14] and triazine, e.g. 2,4,6-tris(trichloromethyl)-l,3,5-triazine ED = borate disulfide, group IVb dimetal [1.15] HD = alcohol, THE, thiol, benzoxazine, aldehyde, acetal, silane (e.g. tris(trime1hylsilyl)silane = (TMS)3Si-H) [1.16]), germane, borane, stannane, alkoxyamine, silyloxyamine, polymer substrate, etc. EPD = amine [1.17], thiol, etc. The generated radicals (e.g. Ph, R, RsSi, RR C R R in [1.13]-[1.17] ) are the initiating species. Efficient novel or newly modified dye structures in the Dye/amine, Dye/iodonium salt or Dye/silane two-component PISs have been proposed within the last 4 years (see section 1.3.5). 

Apart from the II-VI family of materials, the III-Vs are considered one of the most investigated quantum dot materials. Bawendi and co-workers have studied the mechanism for the formation of InP QDs by the reaction of indium (111) myristate, tris(trimethylsilyl)phosphine (TMS)3P and octyl-amine in sealed NMR tubes, analysing the intermediates using NMR spectroscopy. They concluded that InP QDs were formed due to ripening from non-molecular InP species due to the depletion of the phosphorus source in the initial nucleation step, whilst the presence of octylamine prevented the decomposition of the precursor due to solvation effects. 

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