Study of reductions using flow chemistry and catalytic hydroboration of alkenes and alkynes with potassium carbonate(cat.) = Flow chemistry를 이용한 환원 연구와 potassium carbonate를 촉매로 사용한 알켄, 알카인의 촉매 수소화 붕소 첨가 반응

다국어 초록 (Multilingual Abstract)

<Part I>
Due to its high contact efficiency and heat capacity, the flow reactions under micro reactor is known to be highly efficient and reactive than conventional batch systems. Using flow system, with low catalyst load and shorter reaction time an organic reaction can operate with excellent yield. As a result numerous chemical transformations which otherwise difficult to produce in conventional methods were reported by various academies and institutes. As part of our search for efficient reducing agents and selective reductions, and in view of flow technique importance, we made efforts for partial reductions and hydroboration reactions under flow chemistry with ester group. Accordingly, an ester group was reduced with LiOtBu, DIBALH (through the in-situ generated LDBBA), and LiOtBu, MeLi catalyzed hydroboration with pinacolborane.

<Part II>
The importance of green protocols under the environmental concern, cost reduction and simplify of procedures has dawn great attention in recent years. In addition, increased efficacy of the reaction also expected due to the intimacy of the reagents and catalysts used. In this regard, catalytic reactions under minimal solvent or solvent free conditions are becoming most valuable choices in research.
The hydroboration of unsaturated hydrocarbons provides useful synthons for cross-coupling and other important functional transformations. The hydroboration of unsaturated bonds with sodium borohydride-aluminum chloride was first reported by Nobel laureate Prof. H. C. Brown. Later, efforts have been made by several authors to find efficient catalytic system for unsaturated hydroboration (C-C and C=X; X = O, NH). As a result number of catalytic systems including transition metal complexes, main group-alkaline earth metals, and lanthanide complexes were reported.
In the present study, we have taken up the research on transition metal free hydroboration of alkenes and alkynes using lower active reductant such as pinacolborane (HBpin) catalyzed by inexpensive and mild base K2CO3. Accordingly a 1-5 mol% K2CO3 could efficiently provided hydroboration in good yields under solvent free condition.

국문 초록 (Abstract)

Flow chemistry란 반응물을 반응기 내부로 주입시켜 연속적인 흐름을 통해 반응하는 방식이다. 반응기로는 micro reactors가 이용되기도 하는데 부피 대비 표면적이 높은 장점이 있어 열전달 효율 등이 높다. 이러한 장점을 토대로 DIBALH와 lithium tert-butoxide를 이용한 esters의 부분환원 및 methyl lithium 또는 lithium tert-butoxide를 촉매로 이용한 esters의 촉매 수소화 붕소 첨가반응을 flow chemistry에 적용하여 본 결과 batch system 보다 LDBBA의 합성에 효과적임을 알 수 있었다. 그러나 esters의 부분환원 및 촉매 수소화 붕소 첨가반응에서는 기존의 batch system과 비교하여 뚜렷한 장점을 찾을 수 없었다.
수소화 붕소 첨가반응은 유기합성에 중요한 반응으로 최근에는 다양한 촉매를 이용한 촉매 수소화 붕소 첨가반응이 연구되고 있다. 현재까지 불포화 탄화수소의 촉매 수소화 붕소 첨가 반응에 보고된 촉매들은 대부분 비교적 고가의 전이금속을 포함하거나 보관 및 사용이 어려운 강한 친핵성 및 염기성의 시약이 대부분이다. 이와 같은 문제점을 해결하고 보다 효과적인 불포화 탄화수소의 촉매 수소화 붕소 첨가반응을 진행하기 위해 새로운 촉매로 potassium carbonate를 적용시켜 본 결과 알켄으로부터 상응하는 alkyl boronic esters를 알카인의 경우에도 상응하는 vinyl boronic esters를 성공적으로 합성 할 수 있었다.

목차 (Table of Contents)

• <Part I> Study of reductions using flow chemistry
• Ⅰ.Introduction 1
• 1.Flow chemistry 1
• 2.Partial reduction of esters 3
• 3.Hydroboration 5
• 4.Present work 6
• Ⅱ.Experimental section 7
• 1.Preparation of LiOtBu (1.05 M) solution 8
• 2.Preparation of MeLi (0.30 M) solution 8
• 3.Preparation of lithium diisobutyl-t-butoxyaluminum hydride (LDBBA) under batch system 8
• 4.Preparation of ester (0.35 M) solution 9
• 5.Preparation of ester/pinacolborane (1.00 M/3.00 M) mixed solution 9
• 6.General procedure for the partial reduction of ester(batch system) with LDBBA prepared by flow chemistry 9
• 7.Partial reduction of esters by flow chemistry 10
• 8.Hydroboration of esters by flow chemistry 10
• Ⅲ.Results and Discussion 11
• Ⅳ.Conclusion 1
• Ⅴ.References 17
• <Part II> Catalytic hydroboration of alkenes and alkynes with potassium carbonate(cat.)
• Ⅰ.Introduction 18
• 1.The first hydroboration of unsaturated hydrocarbon 18
• 2.The first catalytic hydroboration of unsaturated hydrocarbon 18
• 3.Transition metal catalytic hydroboration of unsaturated hydrocarbon 19
• 4.Main group complex catalytic hydroboration of unsaturated hydrocarbon 21
• 5.Cross-coupling using alkyl boronic esters and vinyl boronic esters 22
• 6.Present work 23
• Ⅱ.Experimental section 24
• 1.Catalytic hydroboration of alkenes 25
• 2.Catalytic hydroboration of alkynes 25
• Ⅲ.Results and Discussion 26
• Ⅳ.Conclusion 32
• Ⅴ.References 33
• 국문초록