Stereoselective synthesis of a new hexanor(C23–C28)castasterone-20,22-ethyl diether from 16-dehydropregnenolone acetate and its plant growth promoting activity

Hazra, Banasri; Basu, Sourav; Bahule, B. B.; Pore, Vandana S.; Vyas, B. N.; Ramraj, V. M.

doi:10.1016/s0040-4020(97)00186-5

Cited by 17 publications

(5 citation statements)

References 28 publications

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“…The alternative route involved introduction of the C6β hydroxyl group via a known two-step sequence consisting of tosylation of 45 and solvolysis under basic conditions, which afforded cyclopropylcarbinol 46 in 80% yield (on a 10 g scale) (Scheme 3A). 41 Subsequent remote radical functionalization of 46 to furnish 47 proved to be far from trivial (Scheme 3B). Surprisingly, when 46 was subjected to the standard Suaŕez (diacetoxyiodo)benzene as the oxidant led to low conversion (entry 5).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Facile Access to Bridged Ring Systems via Point-to-Planar Chirality Transfer: Unified Synthesis of Ten Cyclocitrinols

Wang

Tian

et al. 2019

J. Am. Chem. Soc.

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Bridged ring systems are found in a wide variety of biologically active molecules including pharmaceuticals and natural products. However, the development of practical methods to access such systems with precise control of the planar chirality presents considerable challenges to synthetic chemists. In the context of our work on the synthesis of cyclocitrinols, a family of steroidal natural products, we herein report the development of a point-to-planar chirality transfer strategy for preparing bridged ring systems from readily accessible fused ring systems. Inspired by the proposed pathway for biosynthesis of cyclocitrinols from ergosterol, our strategy involves a bioinspired cascade rearrangement, which enabled the gram-scale synthesis of a common intermediate in nine steps and subsequent unified synthesis of 10 cyclocitrinols in an additional one to three steps. Our work provides experimental support for the proposed biosynthetic pathway and for the possible interrelationships between members of the cyclocitrinol family. In addition to being a convenient route to 5(10→19)abeo-steroids, our strategy also offers a generalized approach to bridged ring systems via point-to-planar chirality transfer. Mechanistic investigations suggest that the key cascade rearrangement involves a regioselective ring scission of a cyclopropylcarbinyl cation rather than a direct Wagner–Meerwein rearrangement.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Facile Access to Bridged Ring Systems via Point-to-Planar Chirality Transfer: Unified Synthesis of Ten Cyclocitrinols

Wang

Tian

et al. 2019

J. Am. Chem. Soc.

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“…The synthesis began with installation of the requisite C6-hydroxyl group in 102. The tosylation of pregnenolone (101) followed by basic solvolysis 91 sequential Pb(OAc) 4 oxidation and BF 3 $Et 2 O-promoted acid solvolysis 92 to generate key intermediate 104 in moderate yield. Phosphorylation of a primary alcohol in 104 gave 105, which was then transformed into p-tolylthio compound 106 by regioselective allylic bromination followed by an S N 2 reaction with p-thiocresol.…”

Section: Rearrangement Biomimetic Cascade Rearrangementmentioning

confidence: 99%

Total Synthesis of Natural Products Containing a Bridgehead Double Bond

Liu

et al. 2020

Chem

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Natural products with a bridgehead double bond, such as taxol and CP molecules, have long attracted considerable attention from chemists because of their promising bioactivity and structural complexity, with the high ring-strain energy in the ring systems representing a formidable synthetic challenge. Herein, strategies for the total synthesis of such complex natural products are reviewed for the first time by using 26 representative studies. Methods for constructing the bridged ring system and bridgehead double bond have been emphasized, including syntheses of the same natural product by different research groups using different strategies, to showcase the diversity of thought and creativity in this area. The total synthesis of these natural products not only provides precious bioactive substances and promising candidates for drug discovery but also has stimulated incredible advances in the development of new strategies and synthetic methods.

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“…[174][175][176][177][178] 16-Dehydropregnenolone, ergosterol and stigmasterol have also provided the starting materials. [179][180][181] The influence of the ring A substituents on the regioselectivity of the Baeyer-Villiger oxidation of ring B has been studied in the context of brassinolide synthesis. 182 The preparation of some biologically active D 5 -7-oxygenated brassinosteroid analogues from stigmasterol has been reported.…”

Section: Cholestanesmentioning

confidence: 99%