On the Mechanism of Gold(I)‐Catalyzed Ring Expansion of Cyclopropanols: Theoretical Calculations Uncover a Bottle‐Neck 1,4‐H Shift and Suggest Adequate Reaction Conditions

Abstract

The mechanism of the one‐carbon ring‐expansion reactions of 1‐(1‐propynyl)cyclopropanol (1; R = Me), (1R*,2R*)‐1‐ethynyl‐2‐isopropylcyclopropanol (3), and (1R*,2S*)‐1‐(phenylethynyl)‐2‐isopropylcyclopropanol (4) catalyzed by [AuP(Ph)3]+ to yield the corresponding 2‐alkylidenecyclobutanones was theoretically investigated by B3LYP‐PCM calculations by using the LANL2DZ relativistic effective core potential for Au and the 6‐31G(d) basis set for the remaining atoms. The most favorable route for these rearrangements in dichloromethane solution is a two‐step mechanism involving as the first step the coordination of the gold(I) complex to the alkyne moiety with subsequent evolution through a 1,2‐alkyl shift. Activation of the reactive C–C bonds takes place mainly through hyperconjugative interactions of these bonds with the oxygen atom and the alkyne moiety; this latter interaction is reinforced by the presence of the cationic gold(I) complex. The second step is the rate‐determining one and consists of a 1,4‐H shift, which requires the assistance by a second molecule of cyclopropanol to become readily accessible. This second molecule plays a very efficient bifunctional catalytic role, which cannot be played by a dichloromethane molecule. The use of methanol, water, and HFIP as assisting molecules was also investigated. Calculations suggest that the process would run most favorably in water. In agreement with experimental data, we found that the most favorable ring expansion of 3 takes place through migration of the substituted carbon atom. The only product to be expected from the rearrangement of 4, however, is that corresponding to the migration of the nonsubstituted carbon atom.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Visible‐Light‐Induced, Manganese‐Catalyzed Tandem Cyclization of 2‐Biphenyl Isocyanides with Cyclopropanols for the Synthesis of 6‐β‐Ketoalkyl Phenanthridines

“…The promising results push us to try the reaction utilizing various Mn catalysts such as Mn 2 (CO) 10 , Mn(OAc) 2 , MnF 3 , MnCl 2 , and MnCO 3 (entries 3-7), unfortunately, no better result was obtained. Next, we investigated the reaction in other solvent, such as t BuOH, MeOH, DMF, 1,4-dioxane, DCE, CH 2 Cl 2 , THF, cyclohexane, and toluene (entries [8][9][10][11][12][13][14][15][16]. Solvent screening showed that protic polar solvent t BuOH and MeOH were also suitable for this reaction.…”

“…Transition-metal-catalyzed cyclopropanol chemistry to construct CÀ C and CÀ X (X = heteroatom) bond has been expanded significantly. [5,[6][7][8][9][10][11][12] Preliminary works mainly cover some precious metals, such as Ru, [6] Pd, [7] Ag, [8] and Au, [9] while recently more involve some inexpensive metals, such as Zn, [10] Cu, [11] Fe, [8d] and Mn. [12] Additionally, earth-abundant Mn complex, Mn(acac) 3 is an inexpensive Lewis acid, which has been widely used in organic synthesis.…”

Non-covalent Interactions Directed Rearrangement of Lactones to Pyrones: A Computational Study on the Mechanistic Insights of Solvent Assisted Gold(I) Catalyzed Reactions

“…The presence of counter ion [11,12] and solvent considered [13][14][15] plays a key role in driving the reaction process. Understanding the mechanism of such reactions is highly challenging and computational studies have always enlightened the chemists to unravel the mechanistic insights for such reactions [9,[16][17][18][19][20]. Reports have shown the importance of non-covalent interactions in directing the reaction path and thereby exemplifying the product formation [21][22][23].…”

“…The counterion OTfH attacks the 'O' proceeding to the carboxylic acid adduct, 1-c via TS3-O-c2 and In7-O-c2.The formation of pyrone can also proceed through 1,3-oxygen shift (Scheme 1). Previous reports on the ring expansion of cyclopropanols suggest a single step for the ring formation[17]. Initially the corresponding transition state which involves the simultaneous breakage of O-C 1 bond and the formation of O-C 2 bond was looked at, which led to futile attempts.…”

Computational Study of the Substitution Effect on the Mechanism for the Gold(I)‐Catalyzed Ring Expansions of Unactivated Alkynylcyclopropanes

“…Notably, the experimental results showed that there must be a hydroxyl group on the cyclopropane ring to make the Toste's and Trost's reactions possible. [10][11][12][13] Therefore, the hydroxyl group on the cyclopropane ring was called the activated group for the ring expansion reaction of the synthesis for cyclobutane derivatives.…”