A Stereodivergent Approach to the Synthesis of gem‐Diborylcyclopropanes

Abstract

We report a designed stereodivergent strategy for the synthesis of gem‐diborylcyclopropanes. The reaction provides a highly modular approach to prepare cyclopropane ring variants bearing gem‐(Bpin,Bpin), gem‐(Bpin,Bdan), and gem‐(Bpin,BF3K), with outstanding levels of stereocontrol. This was achieved by diastereoselective Pd‐catalyzed cyclopropanation reactions of gem‐diborylalkenes with α‐diazoarylacetates and α‐diazoaryl‐trifluoromethyl. The key to the success of this general protocol was the diastereoselective trifluorination reaction of gem‐diborylcyclopropanes, followed by the stereospecific interconversion of the trifluoroborate salts into the Bdan group.

Stereodefined polymetalloid alkenes synthesis via stereoselective boron-masking of polyborylated alkenes

“…We obtained the desired mixed gem -diborylated cycloaddition products 10 and 11 respectively in good yield as described in Fig. 5g 25 , 60 .…”

“…3b . Notably, having this mixed (Bpin,Bdan) unit not only will give the flexibility to tune the reactivity of the boron groups, but also might influence the reactivity of the double bond in alkene-Bdan 2 25 , 60 , 61 .…”

“…Finally, the unsymmetrical gem -diborylalkene 3 was independently subjected to Diels–Alder 25 and the cyclopropanation 60 reactions conditions (Fig. 5g ).…”

Photoredox‐Mediated Deoxygenative Radical Additions of Aromatic Acids to Vinyl Boronic Esters and gem‐Diborylalkenes**

“…[ 12 , 19b , 19c , 20 ] We hypothesized that the preparation of β‐keto‐( gem ‐di)borylalkane via the planned photoredox‐mediated deoxygenated approach[ 2g , 2h , 2i , 10 , 11b ] would be particularly appealing due to the versatility of the carbonyl group, as well as the α‐position to carbonyl and the boryl units, which can be converted to other carbon motifs via modular and programmed transformations (Figure 1 E). [ 14 , 18 , 21 ] However, although several approaches to photo‐activated vinyl boronic esters have been reported,[ 12 , 13 , 16 ] it was unclear whether vinyl boronic esters, for example, 2 , 2 ’ would participate in the proposed photoredox‐mediated deoxygenative transformation, since the boron groups might undergo a sort of complexation with the triphenylphosphine (PPh3), which might prevent this transformation from occurring. However, 11 B NMR and 31 P NMR studies revealed no complexation between the B‐groups and the PPh3 (please see the Supporting Information for details).…”

“…Although applying gem ‐diborylakenes with other boryl groups (i. e., not Bpin group) were unsuccessful, we were alternatively able to convert to the gem ‐(Bpin, Bpin) product for example, 3 a into gem ‐(Bpin, BF3Cs) salt 3 a ‐ BF3 through a selective trifluorination reaction. [ 13 , 21 ]…”