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1. Catalytic asymmetric transformations of racemic α-borylmethyl-( E )-crotylboronate via kinetic resolution or enantioconvergent reaction pathways

   https://doi.org/10.1039/d1sc04047b  

   Gao, Shang; Liu, Jiaming; Chen, Ming (October 2021, Chemical Science)

   We report herein catalytic asymmetric transformations of racemic α-borylmethyl-( E )-crotylboronate. The Brønsted acid-catalyzed kinetic resolution–allylboration reaction sequence of the racemic reagent gave ( Z )-δ-hydroxymethyl- anti -homoallylic alcohols with high Z -selectivities and enantioselectivities upon oxidative workup. In parallel, enantioconvergent pathways were utilized to synthesize chiral nonracemic 1,5-diols and α,β-unsaturated aldehydes with excellent optical purity. 

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2. Highly stereoselective syntheses of ( E )-δ-boryl- anti -homoallylic alcohols via allylation with α-boryl-( E )-crotylboronate

   https://doi.org/10.1039/d1cc04058h  

   Liu, Jiaming; Chen, Ming (October 2021, Chemical Communications)

   A highly stereoselective synthesis of ( E )-δ-boryl- anti -homoallylic alcohols is developed. In the presence of a Lewis acid, aldehyde allylation with α-boryl-( E )-crotylboronate gave δ-boryl- anti -homoallylic alcohols in good yields with excellent E -selectivity. The E -vinylboronate group in the products provides a useful handle for cross-coupling reactions as illustrated in the fragment synthesis of chaxamycins. 

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3. Diastereoconvergent synthesis of anti -1,2-amino alcohols with N-containing quaternary stereocenters via selenium-catalyzed intermolecular C–H amination

   https://doi.org/10.1039/d2sc02648a  

   Zheng, Tianyi; Berman, Janna L.; Michael, Forrest E. (August 2022, Chemical Science)

   We report a diastereoconvergent synthesis of anti -1,2-amino alcohols bearing N-containing quaternary stereocenters using an intermolecular direct C–H amination of homoallylic alcohol derivatives catalyzed by a phosphine selenide. Destruction of the allylic stereocenter during the selenium-catalyzed process allows selective formation of a single diastereomer of the product starting from any diastereomeric mixture of the starting homoallylic alcohol derivatives, eliminating the need for the often-challenging diastereoselective preparation of starting materials. Mechanistic studies show that the diastereoselectivity is controlled by a stereoelectronic effect (inside alkoxy effect) on the transition state of the final [2,3]-sigmatropic rearrangement, leading to the observed anti selectivity. The power of this protocol is further demonstrated on an extension to the synthesis of syn -1,4-amino alcohols from allylic alcohol derivatives, constituting a rare example of 1,4-stereoinduction. 

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4. Stereochemical Control via Chirality Pairing: Stereodivergent Syntheses of Enantioenriched Homoallylic Alcohols

   https://doi.org/10.1002/anie.202107004  

   Gao, Shang; Duan, Meng; Liu, Jiaming; Yu, Peiyuan; Houk, Kendall N.; Chen, Ming (October 2021, Angewandte Chemie International Edition)

   Abstract We report herein the development of stereodivergent syntheses of enantioenriched homoallylic alcohols using chiral nonracemic α‐CH₂Bpin‐substituted crotylboronate. Chiral phosphoric acid (S)‐A‐catalyzed asymmetric allyl addition with the reagent gaveZ‐anti‐homoallylic alcohols with excellent enantioselectivities andZ‐selectivities. When the enantiomeric acid catalyst (R)‐Awas utilized, the stereoselectivity was completely reversed andE‐anti‐homoallylic alcohols were obtained with highE‐selectivities and excellent enantioselectivities. By pairing the chirality of the boron reagent with the catalyst, two complementary stereoisomers of chiral homoallylic alcohols can be obtained selectively from the same boron reagent. DFT computational studies were conducted to probe the origins of the observed stereoselectivity. These reactions generate highly enantioenriched homoallylic alcohol products that are valuable for rapid construction of polyketide structural frameworks. 

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5. Stereoconvergent Synthesis of Z ‐1,3‐Disubstituted‐1,3‐Dienes by Uphill Photocatalysis

   https://doi.org/10.1002/chem.202202635  

   Diver, Steven_T; Glickert, Elise; Rohde, Jr., Laurence_N; Wild, Thérèse (November 2022, Chemistry – A European Journal)

   Abstract A variety of 1‐aryl‐1,3‐dienes were isomerized fromEtoZisomers by photocatalysis using Ru(bpy)₃[PF₆]₂and blue LED light. Enrichment of theZ‐isomer is thought to occur by selective triplet energy transfer from the photocatalyst to the stereoisomeric mixture. The 1,3‐diene starting materials are easily made by catalytic ene‐yne metathesis (EYM). To access 1,3‐dieneZ‐stereoisomers directly, a one pot procedure was developed. Additional 1,3‐dienes were investigated for both isomerization andZ‐enrichment. The combination of cross EYM with photocatalysis allows for the stereoconvergent synthesis ofZ‐1,3‐dienes. 

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