Site-Selective Arylalkane Functionalizations Based On Dehydrogenation Strategy

Alkanes are important basic chemical raw materials and widely exist in fossil resources,yet methodologies for alkanes or alkyl groups transformation to value-added chemicals remain elusive.Most existing methods for alkane transformation rely on the use of alkanes bearing a specific functional group as the directing group,which coordinates with transition metal catalyst and guides the cleavage of one of the C（sp³）–H bonds via cyclometalation.In contrast,the undirected alkyl group functionalizations are much less-explored and usually suffer from poor regio-and stereoselectivity.This dissertation focuses on a series of site-selective functionalizations of arylalkane based on alkane transfer dehydrogenation,enabled by a dual catalyst system.1.Dehydrogenation based asymmetric borylation of benzylic C（sp³）-H bonds.In this part,we developed a dehydrogenation based strategy for enantioselective formal benzylic C（sp³）-H bond borylation through a one-pot,two-step process.Dehydrogenation of arylalkanes by a pincer-Ir complex catalyst produces thermodynamically more stable aryl alkenes via a tandem dehydrogenation-isomerization sequence.The subsequent Cu-catalyzed asymmetric olefin hydroboration affords chiral benzylic boronate esters with excellent site-and enantioselectivity.Moreover,the synthetic utility of these enantioenriched boronates were demonstrated by the synthesis of a series of chiral compounds such as diarylalkanes,alcohols,and potassium trifluoroborate.These transformations generally illustrate the potential for combining alkane dehydrogenation/olefin isomerization with enantioselective olefin hydrofunctionalization to produce enantioenriched fine chemicals directly from hydrocarbon feedstocks.2.Dehydrogenation based asymmetric amination of benzylic C（sp³）-H bonds.In this part,we achieved pincer-Ir complex/diphosphine-Cu catalyzed the enantioselective amination of C（sp³）-H bonds with excellent site-and enantioselectivity,via the sequence of alkane dehydrogenation-olefin isomerization-enantioselective alkene hydroamination.In addition,studies of each step of the relay catalysis provide insights into the role of dual catalysts and the origin of site selectivity.3.Dehydrogenation based arene-alkane couplings.In this part,we describe a one-pot relay bimetallic catalysis system for formal arene-alkane couplings involving（pincer）Ir-catalyzed alkane transfer dehydrogenation and Fe-catalyzed olefin hydroarylation.This catalytic system exhibits broad scope and is particularly effective for arylalkanes to form 1,1-diarylalkanes with good chemo-and regioselectivity,making it possible for late-stage alkylation of complex molecules.Finally,the strategy of dehydrogenation-enabled arene-alkane couplings has been successfully extended to tandem catalysis by using a heterogeneous olefin hydroarylation catalyst.4.Dehydrogenation based arylalkanes borylation ofβ-site C（sp³）-H bonds.In this part,we developed a formal borylation of arylalkanes atβ-site C（sp³）-H bonds with excellent site selectivity and moderate to high yields by using pincer iridium complex as alkane transfer dehydrogenation catalyst and FeCl₂as hydroboration catalyst.This catalytic system provides a new synthetic approach for b-position branched alkyl boronate esters.