Synthesis of Cyclic Bis(trimethysilyl) Enol Ethers and Their [3 + 4] and [3 + 5] Annulation Reactions with Dicarbonyl Electrophiles. Access to Highly Functionalized Tricyclic Ethers Possessing Trans Intrabridgehead Stereochemistry

Abstract

The synthesis of cyclic bis(trimethylsilyl) enol ethers from cycloalkanone carboxylates is described. The [3 + 4] and [3 + 5] annulation reactions of these bis(dinucleophilic) synthons with various 1,4- and 1,5-dicarbonyl electrophiles leads to the formation of tricyclic keto ethers with good regio- and stereochemical control. An interesting trans intrabridgehead stereochemistry is observed when using bis(trimethylsilyl) enol ethers derived from nine- to 12-membered ring β-keto esters.

Domino Reactions of 1,3‐Bis‐Silyl Enol Ethers with Benzopyrylium Triflates: Efficient Synthesis of Fluorescent 6H‐Benzo[c]chromen‐6‐ones, Dibenzo[c,d]chromen‐6‐ones, and 2,3‐Dihydro‐1H‐4,6‐dioxachrysen‐5‐ones

“…The reaction of cyclic 1,3‐bis‐silyl enol ether 3 n 22 with 1 a afforded the condensation product 4 ae as a mixture of diastereomers and keto/enol tautomers (Scheme ); to simplify the NMR spectra, 4 ae was transformed into the silyl enol ether 4 af . Only starting material was recovered in the reaction of 4 ae with NEt 3 /EtOH.…”

Synthesis of 2-Alkylidenepyrrolidines, Pyrroles, and Indoles by Condensation of Silyl Enol Ethers and 1,3-Bis-Silyl Enol Ethers with 1-Azido-2,2-dimethoxyethane and Subsequent Reductive Cyclization

“…The reaction of cyclic 1,3-bis-silyl enol ethers with 1-azido-2,2-dimethoxyethane ( 2 ) was studied next (Scheme , Table ). The reaction of 2 with 1p , prepared from ethyl cyclododecan-1-one-2-carboxylate, afforded the condensation product 3p with good 1,2-diastereoselectivity.…”

Regioselective Synthesis of Medium-Sized Bicyclic Butenolides by Lewis Acid Catalyzed Cyclization of Cyclic 1,3-Bis(trimethylsilyloxy)-1,3-butadienes with Oxalyl Chloride

“…Reaction of the dianion of ethyl cyclohexanone-2-carboxylate 1a (generated by means of 2 equiv of LDA) with N , N ‘-dimethoxy- N , N ‘-dimethylethanediamide 2a , the Weinreb amide of oxalic acid,6a resulted in the formation of a complex mixture rather than the desired butenolide 4a (Scheme ). Therefore, we have envisaged a Lewis acid-catalyzed synthesis of butenolide 4a via the 1,3-bis(trimethylsilyloxy)-1,3-butadiene 3a which represents an electroneutral dianion equivalent. 6c,

1

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“…However, these compounds could be prepared by a known one-step synthesis: 7d,8 the dianions of 1a − i were generated by treatment of the 1,3-dicarbonyl compounds with 2 equiv of LDA. Addition of Me 3 SiCl, stirring for 2 h at 0 °C and subsequent nonaquoeus workup afforded the 1,3-bis(trimethylsilyloxy)-1,3-butadienes 3a − d and 3f − i in high yields 7d. In the five-membered ring case, a 2:1 mixture of 3e and of a monosilyl enol ether was obtained.…”

“…In the five-membered ring case, a 2:1 mixture of 3e and of a monosilyl enol ether was obtained. The reaction of Me 3 SiCl with dianions of open-chain β-keto esters has been reported to result in significant silylation of the terminal carbon atom of the dianion 7b…”