Time and Pot Economy in Total Synthesis

We would all like to make or obtain the materials or products we want as soon as possible. This is human nature. This is true also for chemists in the synthesis of organic molecules. All chemists would like to make their target molecules as soon as possible, particularly when their interest is in the physical or biological properties of those molecules.As demonstrated by today's COVID-19 (SARS-CoV-2) pandemic, rapid synthesis is also crucial to enable chemists to deliver effective therapeutic agents to the community. Several concepts are currently well-accepted as important for achieving this: atom economy, step economy, and redox economy. Considering the importance of synthesizing organic molecules rapidly, I recently proposed adding the concept of time economy.In a multisep synthesis, each step has to be completed within a short period of time to make the desired molecule rapidly. The development of rapid reactions is important but also insufficient. After each step, frequent and repetitive workup operations such as quenching the reaction, extraction, separation of water and organic phases, drying the organic phase, filtration, evaporation, and purification may be required, and the time necessary for these processing operations must be taken into account. Indeed, some of the most time-consuming operations in most syntheses are the purification stages.On the other hand, one-pot reactions are processes in which several sequential reactions are conducted in a single reaction vessel, which avoids the need to purify intermediates. One-pot reactions are a useful way to shorten the total synthesis time, and the approach generally leads to an increase in the yield and a reduction in the amount of chemical waste formed. Thus, I also propose the importance of pot economy.On the basis of these concepts of time and pot economy, we have accomplished efficient syntheses of several natural products and medicines. The key to the success of these syntheses is the use of diphenylprolinol silyl ether as an effective catalyst in a one-pot reaction, in which it does not disturb the subsequent reactions. Our strategy is (1) to construct the chiral key skeletons and/or key components of natural products and medicines directly using organocatalyst-mediated one-pot reactions and (2) to conduct the subsequent transformations to the final molecules in a small number of pots utilizing the internal quench method. By means of this strategy, PGE₁ methyl ester, estradiol methyl ether, and clinprost were synthesized in three, five, and seven pots, respectively. Furthermore, (-)-oseltamivir, ABT-341, baclofen, and Corey lactone were synthesized in a single reaction vessel. Further optimization of the reactions in terms of time economy allowed (-)-oseltamivir and Corey lactone to be synthesized within 60 and 152 min, respectively. These syntheses will be highlighted as case studies. Although the organocatalyst is a key compound in this Account, pot- and time-economical syntheses can be expanded to organometallic chemistry and, indeed, to organic chemistry in general.

Synthesis of 2-aminopyridines via ruthenium-catalyzed [2+2+2] cycloaddition of 1,6- and 1,7-diynes with cyanamides: scope and limitations

A direct route to access 2-aminopyridines using Ru-catalyzed-[2+2+2] cycloaddition of 1,n-diynes with cyanamides is described in excellent yields and regioselectivities.

Pot Economy in the Total Synthesis of Estradiol Methyl Ether by Using an Organocatalyst

Enantioselective total synthesis of estradiol methyl ether has been accomplished in a pot-economical manner using five reaction vessels and four purifications. The key reaction is a diphenylprolinol silyl ether mediated domino Michael/aldol reaction to afford bicyclo[4.3.0]nonane derivatives, containing the A, C, and D rings of steroids, as a single isomer with excellent enantioselectivity. Six reactions such as oxidation, hydrogenation, formation of acid chloride, Friedel-Crafts reaction, deprotection, and reduction can be carried out in the last one-pot sequence.

Diastereoselective Pt catalyzed cycloisomerization of polyenes to polycycles

Application of a tridentate NHC containing pincer ligand to Pt catalyzed cascade cyclization reactions has allowed for the catalytic, diastereoselective cycloisomerization of biogenic alkene terminated substrates to the their polycyclic counterparts.

Gold(I)-catalyzed formation of bicyclo[4.2.0]oct-1-enes

Gold(I) catalysts effectively promote the Cope rearrangement of acyclic 1,5-dienes bearing a terminal cyclopropylidene. When this methodology is applied to cyclic substrates an unexpected transformation occurs, resulting in the formation of a tricyclic compound incorporating a bicyclo[4.2.0]oct-1-ene core, a portion of which is found in a number of natural products. Density functional theory calculations (M06 and M06-2X) reveal insight into the mechanism and thermodynamics of this unique transformation.

Catalytic platinum-initiated cation-olefin reactions with alkene terminating groups

A series of phosphine-Pt(2+)-catalysts is reported, which enable the oxidative cascade cyclization of poly-alkene substrates. When the terminus is appropriately arranged and a catalyst reoxidation mediator is included, several polycyclic all carbon skeletons can be obtained. In one example, a chiral P2Pt(+2) catalyst provides up to 79% ee.