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Abstract Alkenes are a central part of organic chemistry^1–3. However, although most alkenes are easy to prepare, the controlled synthesis of tetrasubstituted alkenes, those with four groups around the central C=C bond, remains challenging^1–5. Here we report the boron-mediated assembly of tetrasubstituted alkenes with complete control of the double-bond geometry. The migrating group and electrophile add syn across the alkyne. Mild oxidation leads to intermediate borinic esters⁶, which can be isolated and purified or reacted directly in a range of transformations, including cross-couplings and homologation reactions. In particular, subjecting the intermediate borinic esters to Zweifel^7,8olefination conditions can give either retention or inversion of the double-bond geometry, depending on whether base is present or not. Different positional and stereoisomers of the tetrasubstituted alkenes can be easily accessed, highlighting the breadth and versatility of the method. This was showcased through its successful application to the rapid synthesis of drug molecules and natural products with high yield and stereocontrol. Not only does this method provide efficient access to the long-standing challenge of the stereocontrolled synthesis of tetrasubstituted alkenes but it also introduces new concepts related to the intervention of non-classical borenium ions in the Zweifel olefination. 

Abstract Asymmetric diboration of terminal alkenes is well established, and subsequent selective functionalization of the less hindered primary boronic ester is commonly achieved. Conversely, selective functionalization of the sterically less accessible secondary boronic ester remains challenging. An alternative way to control chemoselective functionalization of bis(boron) compounds is by engendering different Lewis acidity to the two boryl moieties, since reactivity would then be dictated by Lewis acidity instead of sterics. We report herein the regio‐ and enantioselective Pt‐catalyzed diboration of unactivated alkenes with (pin)B−B(dan). A broad range of terminal and cyclic alkenes undergo diboration to furnish the differentiable 1,2‐bis(boron) compounds with high levels of regio‐ and enantiocontrol, giving access to a wide variety of novel building blocks from a common intermediate. The reaction places the less Lewis acidic B(dan) group at the less hindered position and the resulting 1,2‐bisboryl alkanes undergo selective transformations of the B(pin) group located at the more hindered position. The regioselectivity of the diboration has been studied by DFT calculations and is believed to originate from thetransinfluence, which lowers the activation barrier for formation of the regioisomer that places the weaker electron donor [B(pin) vs B(dan)] opposite the strong electron donor (alkyl group) in the platinum complex.