Beeraiah Baire

The Z-enoate assisted, Meyer–Schuster rearrangement cascade: unconventional synthesis of α-arylenone esters

Brønsted acid promoted nucleophilation of propargylic alcohols during the Meyer-Schuster rearrangement (M-S) has been introduced. A novel concept of reverse polarization of the M-S intermediate allenyl cation has been realized by employing a cis-enoate assisted strategy. This idea is well demonstrated by the metal free synthesis of complex, highly functionalized cyclic as well as acyclic α-arylenones. The synthetic importance of the derived products was highlighted by the efficient conversion to biologically relevant molecules such as pyrazoles and 4,5-seco-abietane.

Mild Approach to 2-Acylfurans via Intercepted Meyer–Schuster Rearrangement of 6-Hydroxyhex-2-en-4-ynals

We have developed a mild, intramolecular intercepted Meyer-Schuster (M-S) rearrangement for the synthesis of 2-acylfurans from corresponding cis-6-hydroxyhex-2-en-4-ynals. This reaction was found to be very general, and the starting materials are easily accessible. By this methodology the first synthesis of deoxy-nor-abiesesquine B, a sesquiterpene, was also achieved in three steps. The concept of adding two nucleophiles during the M-S rearrangement was introduced.

Stereoselective, Cascade Synthesis of trans-Enynones through Coupling-Isomerization Reaction

A mild, cascade methodology based on the modified Cadiot-Chodkiewicz reaction was developed for the stereoselective synthesis of trans-enynones. By this methodology, structurally divergent trans-enynones, which are embedded with sensitive functional groups, were synthesized. Control experiments suggested that the CuCl alone does not have a role in the isomerization step, whereas the CuCl-piperidine complex (formed during the cross coupling) may have a rate enhancing effect. Furthermore, additional sets of control experiments favor the involvement of unimolecular [1,2]-H shift rather than a homobimolecular proton abstraction during the isomerization step.

Regioselective, cascade [3+2] annulation of β-naphthols (resorcinols) with Z-enoate propargylic alcohols: a novel entry for the synthesis of complex naphtho(benzo)furans

An acid promoted, unprecedented cascade [3+2] annulation strategy for the synthesis of complex naphtho- and benzofurans is reported. An alkoxyfuranylallene intermediate (generated from Z-enoate propargylic alcohols via a Meyer-Schuster rearrangement) was employed as the 1,2-bis-electrophile and β-naphthols (phenols) as 1,3-bisnucleophiles. This strategy represents the first cascade and metal free process for the synthesis of naphthofurans and benzofurans from propargylic alcohols. A very broad substrate scope was observed. The synthesized naphtho- and benzofurans were efficiently transformed into the frameworks of the bioactive natural products amycofuran and frondosin B.

Unconventional Reactivity of (Z)-Enoate Propargylic Alcohols in the Presence of Acids

The unconventional reactivity of (Z)-enoate-attached propargylic alcohols in the presence of acids (nucleophilic and non-nucleophilic) was described. This study led to the discovery and development of a new strategy for the collective synthesis of the synthetically useful building blocks α-OMs-, α-OTs-, and α-Cl-enones, as well as 4,5-dioxonoates. The reaction proceeded under very mild conditions and showed a broad substrate scope.

A systematic study on the Cadiot–Chodkiewicz cross coupling reaction for the selective and efficient synthesis of hetero-diynes

Mild reaction conditions for the Cadiot–Chodkiewicz cross coupling process have been developed for the highly selective and efficient synthesis of unsymmetrical diynes. The most abundant, economic, environmentally friendly, green solvent, water was employed as the sole reaction medium in combination with a minimal amount (5 equiv.) of piperidine base. The reported new reaction conditions provide operational simplicity, high selectivity for hetero coupling (>97%), use of water, and low basicity of the reaction medium compared to commonly used highly basic conditions, i.e., 30–70% amine in water or 100% piperidine. Various sensitive functional groups were found to be highly compatible with the developed low basic reaction conditions. This study supports the fact that the Cadiot–Chodkiewicz cross coupling can be a greener reaction, has a very broad substrate scope, but has always been employed in non-green highly basic conditions and with limited substrate scope.

Regioselective Cyclization of (Indol-3-yl)pentyn-3-ols as an Approach to (Tetrahydro)carbazoles

An acid-catalyzed, highly regioselective cycloisomerization as well as dehydro-cyclization of (indol-3-yl)pentyn-3-ols has been reported for the selective synthesis of tetrahydrocarbazoles and carbazoles. This process is mild and found to be very general in terms of structural diversity of substrates. Utilizing the strategy, an efficient synthetic approach for the functionalized frameworks of carbazomycins A-D has also been developed.

An Unprecedented (Semi)Favorskii Rearrangement. Evidence for the 2-(Acyloxy)cyclopropanones

Discovery and development of an unprecedented (semi)Favorskii rearrangement has been reported. The intermediacy of structurally singular (acyloxy)cyclopropanones has been unraveled by fruitful control experiments including a crossover experiment. This class of cyclopropanones is found to be inert for classical Favorskii functionalization and preferably undergoes a decycloisomerization (ring-chain valence tautomerism) to α-(acyloxy)enones. A cascade conversion of α,α-diiodo-α-acetoxyketones to (acyloxy)cyclopropanones via α-iodo-α-acetoxyketones has been achieved by the synchronous dual basicity (Lewis and Brønsted) of amines. The overall process is found to be very general for diverse substrates and highly efficient.