Isothiourea-Mediated Organocatalytic Michael Addition–Lactonization on a Surface: Modification of SAMs on Silicon Oxide Substrates

Abstract

Tailoring the functionality of self-assembled monolayers (SAMs) can be achieved either by depositing prefunctionalized molecules with the appropriate terminal groups or by chemical modification of an existing SAM in situ. The latter approach is particularly advantageous to allow for diversity of surface functionalization from a single SAM and if the incorporation of bulky groups is desired. In the present study an organocatalytic isothiourea-mediated Michael addition-lactonization process analogous to a previously reported study in solution is presented. An achiral isothiourea, 3,4-dihydro-2H-pyrimido[2,1-b]benzothiazole (DHPB), promotes the intermolecular Michael addition-lactonization of a trifluoromethylenone terminated SAM and a variety of arylacetic acids affording C(6)-trifluoromethyldihydropyranones tethered to the surface. X-ray photoelectron spectroscopy, atomic force microscopy, contact angle, and ellipsometry analysis were conducted to confirm the presence of the substituted dihydropyranone. A model study of this approach was also performed in solution to probe the reaction diastereoselectivity as it cannot be measured directly on the surface.

Direct Organocatalytic Enantioselective Functionalization of SiOx Surfaces

“…There is virtually no azide signal visible in the N 1s region at about 404.5 eV. Therefore, we estimate the conversion from the azide into the enone to be greater than 90 % …”

“…An estimate of the conversion from the enone into lactone can be obtained from the ratio of the O=C−O/C−F signals (green) and the CF 3 signal (red), thus indicating about 37 % conversion (for details see the Supporting Information). A conversion of about 41 % was observed when using the achiral catalyst DHPB . XPS spectra for chiral surfaces prepared by Michael lactonization with the catalyst (2 R ,3 S )‐HyperBTM are shown in the Supporting Information, and give very similar enone to lactone conversions.…”

“…Catalytic functionalization of the enone‐terminated SAM was achieved using an isothiourea‐mediated organocatalytic Michael addition/lactonization process. Using an achiral isothiourea catalyst, DHPB (3,4‐dihydro‐2 H ‐pyrimido[2,1‐ b ]benzothiazole), allowed the preparation of a variety of racemic lactone‐terminated SAMs (in approximately 40–50 % enone to lactone conversion) on SiO x substrates, and they were characterized by XPS, ellipsometry, contact‐angle goniometry, and AFM . Herein, both enantiomers of a chiral isothiourea, HyperBTM, are used to promote direct catalytic enantioselective functionalization of the trifluoromethylenone‐terminated surface (see Figure c).…”

On-Surface Modification of Copper Cathodes by Copper(I)-Catalyzed Azide Alkyne Cycloaddition and CO2 Reduction in Organic Environments

“…XPS analysis of the Cu_3E+3A-modified Cu surface showed that a fair amount of nitrogen was introduced onto the surface (Figure 4). The binding energy associated with the introduced N species does not indicate an azide moiety, as this exhibited a peak located at ∼405 eV (Collman et al, 2006;Chisholm et al, 2016). The majority of the nitrogen, when affixed to the surface, appeared in the form of a triazole.…”

Sulfamide chemistry applied to the functionalization of self-assembled monolayers on gold surfaces

“…The seminal work of Nuzzo and Allara on the adsorption of disulfides on gold surface has triggered numerous research activities in the preparation and applications of sulfur-based SAMs on Au surfaces [4]. Important contributions have been notably driven by the implementation of reactive end groups in the monolayers enabling the chemical functionalization of solid surfaces [3,5–7]. Within this context, noncovalent and covalent strategies have been investigated for the immobilization of a target molecule through a reaction with the terminal groups of the SAMs.…”