Methods for the construction of trans-hydrindane rings and their origins in steroid chemistry. Vitamin D total synthesis

An enantioselective desymmetrisation approach to C9-substituted trans-hydrindene rings based on a diastereotopic group-selective intramolecular Diels–Alder reaction

The synthesis of an achiral skipped bis(1,3-diene) substrate was achieved, which was shown to undergo an enantioselective, diastereotopic group-selective, intramolecular Diels-Alder reaction.

Dual Behavior of Masked o-Benzoquinones in Intermolecular Diels−Alder Reactions with Acyclic Dienes: A Rapid Entry to Polyfunctionalized Bicyclo[2.2.2]oct-5-en-2-ones and cis-Decalins

The potentiality of the masked o-benzoquinones, i.e., 6,6-dimethoxy-2,4-cyclohexadienones 5-8, to react both as dienes and dienophiles in their intermolecular reactions has been demonstrated. The masked o-benzoquinones (MOBs) 5-8 generated in situ from 2-methoxyphenols 1-4 underwent intermolecular Diels-Alder cycloadditions with acyclic 1,3-dienes 9a-e to provide bicyclo[2.2.2]octenones 10a-f-13a-f along with cis-decalin derivatives 14a-f-17a-f with regio- and stereoselectivity, except in the case of MOB 8. The formation of cis-decalins in these Diels-Alder reactions illustrates the dienophilic character of MOBs, in addition to their general behavior as dienes. The ratio of the two cycloadducts obtained in each reaction as a result of the dual character of MOBs depends on the nature and/or position of the substituents on both the cyclohexadienone moiety and the added conjugated acyclic diene. All of the cycloadducts resulted from the diene property of MOBs in intermolecular Diels-Alder reactions smoothly underwent Cope rearrangement to furnish cis-decalins as sole products in excellent to quantitative yields.

Simple construction of bicyclo[4.3.0]nonane, bicyclo[3.3.0]octane, and related benzo derivatives by palladium-catalyzed cycloalkenylation

[reaction: see text] Bicyclo[4.3.0]nonanes (hydrindanes) and bicyclo[3.3.0]octanes (octahydropentalenes) are easily synthesized by palladium-catalyzed cycloalkenylations. Additionally, benzo-fused bicyclo[3.3.0]octanes are prepared for the first time through intramolecular coupling between silyl enol ethers and aromatic rings in the presence of catalytic palladium acetate.

Synthesis of (-)-astrogorgiadiol

Reaction of Rh2(S)-PTPA4 with the (R)-citronellol-derived alpha-diazo-beta-ketoester 1 led to the formation of cyclic beta-ketoester 2 in 95% yield and 48% diastereomeric excess. The purity of 2 was increased to > 99% de after one crystallization. To demonstrate its utility in steroid total synthesis, the beta-ketoester 2 was carried on to secosteroid (-)-astrogorgiadiol (3), a naturally occurring vitamin D analogue with antiproliferative properties.