Selective P450BM3 Hydroxylation of Cyclobutylamine and Bicyclo[1.1.1]pentylamine Derivatives: Underpinning Synthetic Chemistry for Drug Discovery

tert-Butyl as a Functional Group: Non-Directed Catalytic Hydroxylation of Sterically Congested Primary C-H Bonds

The tert-butyl group is a common aliphatic motif extensively employed to implement steric congestion and conformational rigidity in organic and organometallic molecules. Because of the combination of a high bond dissociation energy (~100 kcal mol-1) and limited accessibility, in the absence of directing groups, neither radical nor organometallic approaches are effective for the chemical modification of tert-butyl C-H bonds. Herein we overcome these limits by employing a highly electrophilic manganese catalyst, [Mn(CF3bpeb)(OTf)2], that operates in the strong hydrogen bond donor solvent nonafluoro-tert-butyl alcohol (NFTBA) and catalytically activates hydrogen peroxide to generate a powerful manganese-oxo species that effectively oxidizes tert-butyl C-H bonds. Leveraging on the interplay of steric, electronic, medium and torsional effects, site-selective and product chemoselective hydroxylation of the tert-butyl group is accomplished with broad reaction scope, delivering primary alcohols as largely dominant products in preparative yields. Late-stage hydroxylation at tert-butyl sites is demonstrated on 6 densely functionalized molecules of pharmaceutical interest. This work uncovers a novel disconnection approach, harnessing tert-butyl as a potential functional group in strategic synthetic planning for complex molecular architectures.

Light-Driven Synthesis and Functionalization of Bicycloalkanes, Cubanes and Related Bioisosteres

Bicycloalkanes, cubanes and their structural analogues have emerged as bioisosteres of (hetero)arenes. To meet increasing demand, the chemical community has developed a plethora of novel synthetic methods. In this review, we assess the progress made in the field of light-driven construction and functionalization of such relevant molecules. We have focused on diverse structural targets, as well as on reaction processes giving access to: (i) [1.1.1]-bicyclopentanes (BCPs); (ii) [2.2.1]-bicyclohexanes (BCHs); (iii) [3.1.1]-bicycloheptanes (BCHeps); and (iv) cubanes; as well as other structurally related scaffolds. Finally, future perspectives dealing with the identification of novel reaction manifolds to access new functionalized bioisosteric units are discussed.

Routes to Advanced Intermediates in the Synthesis of Tetracarbocyclic Sesquiterpenoids Daphnenoid A and Artatrovirenols A and B

A short route from dihydrocarvone is described, which led to the tetracarbocyclic core common to artatrovirenol A and B and daphnenoid A. A variant of this route afforded guaia-4,6-dien-3-one (from Enterospermum madagascarensis) and its epimer. From 2-(2-oxoethyl)furan, a 15-step sequence then delivered the complete carbon skeleton and all functionality necessary for daphnenoid A. Key steps in the route include diastereoselective intramolecular oxidopyrylium cycloaddition, oxa-bridge cleavage under "push-pull" conditions, and intramolecular Diels-Alder cycloaddition.