8.26 Reduction of Saturated Alkyl Halides to Alkanes

Thirty Years of (TMS)3SiH: A Milestone in Radical-Based Synthetic Chemistry

“…In this section, the pure dehalogenation will be examined, whereas the dehalogenation that precedes the C−C bond forming will be treated in section 5. The reduction of alkyl halides to alkanes can be achieved by different methodologies, radical and nonradical ones, 26 whereas the use of silyl radical-mediated reductions introduced several advantages of selectivity, flexibility, and tolerability, which are highlighted in the examples given in this section.…”

“…Bromine reduction is an important step in the natural product synthesis, and the use of TTMSS brought an advantage for the ease and cleanliness of such reaction. , An example is shown with the strategy for naturally occurring lactones, where the bromolactonization reaction was realized in an asymmetric version that affords the compounds with high enantiopurity, then leaving the task of the bromine elimination. The debromination of 15 is shown in Scheme , where the solid product 16 was recrystallized (heptane:EtOAc = 95:5), raising the enantiomeric excess to >99% …”

Completing the β,γ-CXY-dNTP Stereochemical Probe Toolkit: Synthetic Access to the dCTP Diastereomers and 31P and 19F NMR Correlations with Absolute Configurations

“…32,43 Although the (R)-mandelate bisphosphonic acid P,Cdimorpholinamide synthon also provides access to the individual β,γ-CHX-dATP (X = F, Cl) and β,γ-CHCl-dTTP diastereomers as detailed here (Scheme 1), it involves a catalytic hydrogenation deprotection step that could be problematic with the cytosine heterocycle in CTP and also leads to reduction of the bromo substituent in β,γ-CHBr-dNTP analogues. 44,45 To complete assembly of a β,γ-CXY-dNTP toolkit encompassing all four DNA bases and including β,γ-CHBr-dNTPs, we report here an alternative synthetic route featuring the novel chiral BP synthons 22a, 22b, 23a, 23b, 24a, and 24b (Figure 4C). After acid-catalyzed removal of the (R)-(+)-α-ethylbenzylamine auxiliary, coupling with activated dCMP and photochemical deprotection, the individual β,γ-CHBr− (33a, 33b), β,γ-CHCl− (34a, 34b), and β,γ-CHF-dCTP (35a, 35b) diastereomers (Scheme 2) are obtained in modest yield.…”

Defunctionalization of sp3 C–Heteroatom and sp3 C–C Bonds Enabled by Photoexcited Triplet Ketone Catalysts

“…Over the last decades, traditional catalysis science has primarily focused on the discovery of new methods for forging sp 3 C–C and C–heteroatom bonds in a chemo-, regio-, and enantioselective manner (Scheme , path a) . In contrast, sp 3 defunctionalization reactions have commonly been perceived as a trivial scenario, as it formally incorporates a hydrogen atom into an alkyl side chain (path b) . However, these techniques can be considered in many instances as even more challenging and relevant than traditional endeavors from both a mechanistic and significance standpoint because of (a) the high energy input required for activating σ sp 3 C–C­(heteroatom) linkages, (b) the inherent interest in converting environmentally hazardous halogenated entities–used extensively in fire extinguishants or pesticides–into harmless materials and/or (c) the opportunity of preparing hydrocarbons for fuels and chemical feedstocks via valorization of overfunctionalized biomass molecules or native functionalities, thus offering a worthwhile endeavor for chemical innovation.…”