Ruthenium-Catalyzed Intramolecular Double Hydroalkoxylation of Internal Alkynes

Abstract

Intramolecular double hydroalkoxylation of internal alkynes could be achieved using a Grubbs-type ruthenium carbene complex or its modified species to deliver a series of bridged-and spiroacetal derivatives in moderate to good yields. This study represents a new example of nonmetathetic reactions catalyzed by Grubbs-type ruthenium carbene complexes.

Ruthenium-Catalyzed Intramolecular Double Hydrofunctionalization of Alkynes. Synthesis of Spirocyclic Hemiaminal Ethers and Their Lewis Acid-Mediated Cleavage/Nucleophilic Addition

“…We have previously reported that the second-generation Hoveyda–Grubbs ( HG-II ) complex modified with DMF enables intramolecular double hydroalkoxylation of internal alkynes to provide a series of bridged- and spiroacetals in moderate to good yields (Scheme ). As an extension of our previous work, we envisioned that it might be similarly possible to synthesize spiroaminals under ruthenium catalysis. , Several groups have independently described gold-catalyzed alkyne double hydrofunctionalization for spiroaminal synthesis. , …”

“…Alkynes 1l–1o were prepared from homopropargylic alcohols 20a , b . Mesylation of 20a , b followed by azide displacement provided the corresponding azides, which were reduced with zinc (NH 4 Cl, THF/H 2 O, 50 °C) and then protected with TsCl/pyridine to deliver sulfonamides 21a , b .…”

“…Meanwhile, aliphatic alkynes 1g , h were more reactive than aromatic alkynes 1a , b toward the ruthenium-catalyzed double hydrofunctionalization and delivered spiroaminals 24g in 79 and 87% yields, respectively. The reactivity difference observed between aliphatic and aromatic alkynes is in accordance with our previous observation on alkyne diols . One-carbon homologated aliphatic alkynes 1i , j were also good substrates for the reaction and provided spiroaminals 24i , j in 60 and 65% yields, respectively.…”

Transition Metal‐Catalyzed Hydroalkoxylation of Alkynes: An Overview

“…On similar lines, Fuwa et al reported ruthenium-catalyzed double hydroalkoxylation of alkynyl diols 115 for the synthesis of bridge bicyclic dioxanes 116 in excellent yield (Scheme 46). [52] In these cases, aliphatic as well as aromatic alkynes gave good yields. However, an aromatic ring with electron-withdrawing groups indeed furnished a very less amount of product.…”

Preparation of benzannulated spiroketals by gold(III) catalyzed spirocyclization of alkynyl diols

“…Lately, a cycloisomerization approach by intramolecular dihydroalkoxylation of alkynyl diols catalysed by various transition metals such as Pd(II), Pt(II), Ir(I), Rh(I), Ru(II) and Au(I/III) has emerged as a more selective strategy. [11][12][13][14] This method offers specific advantages, as the alkyne acts as a masked carbonyl group, and the non-polar alkyne π-bonds being more compatible than ketones towards a number of common reaction conditions. 15 Gold catalysis has been a rapidly emerging field within transition metal catalysis in the past decade.…”