Gopal Bose

A useful and convenient synthetic protocol for interconversion of carbonyl compounds to the corresponding 1,3-oxathiolanes and vice versa employing organic ammonium tribromide (OATB)☆

A wide variety of carbonyl compounds 1 can be easily protected selectively as the corresponding 1,3-oxathiolanes 2 in good yields using a catalytic amount (0.01–0.1 equiv.) of n-tetrabutylammonium tribromide in dry CH2Cl2 at 0–5 °C. On the other hand, various 1,3-oxathiolanes 2 can be deprotected chemoselectively to the parent carbonyl compounds 1 employing 0.5 equivalents of organic ammonium tribromides under identical conditions in very high yields. Mild conditions, high selectivity and yield, highly efficient, less expensive, and no brominations either at the double bond or allylic position and even α- to the keto position or aromatic ring are some of the major advantages of the protocol.

Birch reductive alkylation of biaryls: scope and limitations.

Birch reductive alkylation of biaryls has been carried out by varying the nature of the substituents on the aromatic rings. Our investigations have focused on electron-rich substituents such as OMe, OH, and NR(2) groups as they are present on the skeleton of targeted alkaloids. The regioselectivity is strongly affected by the electronic nature of these substituents on both rings. The 3,5-dimethoxyphenyl moiety is selectively reduced and then alkylated, while phenols and anilines do not react under these conditions. A biaryl possessing both a 3,5-dimethoxyphenyl moiety and a phenol ring may, however, be reduced and alkylated provided the acidic phenolic proton is removed prior to the treatment with Li in NH(3). Similarly, biaryls possessing a o-sulfonamide group are reduced regioselectively and alkylated with alpha-chloroacetonitrile or N-tosylaziridine to provide the corresponding dienes in reasonable to good yields. A survey of the alkylating agents was also performed showing that various functional groups may be introduced at the benzylic position, including esters, primary and tertiary amides, nitriles, epoxides, and acetals and also unfunctionalized sterically hindered t-Bu groups and cyclopropyl substituents. The introduction of the latter indicates that both a S(N)2 and a SET mechanism may take place during the alkylating step.

An exceptionally simple and catalytic method for regeneration of carbonyl functionality from the corresponding 1,3-oxathiolanes

A wide variety of 1,3-oxathiolanes 1 can be chemoselectively deprotected to the corresponding carbonyl compounds 2 in good yields by employing V2O5–H2O2 catalyzed oxidation of ammonium bromide in a CH2Cl2–H2O mixture at 0–5 °C. Some of the major advantages of this procedure are its mild conditions, and that it is highly selective and efficient, high yielding, and cost-effective. Furthermore, no brominations occur at the double bond or allylic position or α to the keto position or aromatic ring.

Straightforward assembly of the octahydroisoquinoline core of morphinan alkaloids.

The octahydroisoquinoline core of morphinan was assembled starting from readily available arylcyclohexadienes. Three different approaches were developed, including a metal- and an acid-mediated Mannich type process and an anionic-mediated cyclization. All provided the desired motif as a single diastereomer having a C9-C13-C14 trans-cis relative configuration.