Silazanes/catalytic bases: mild, powerful and chemoselective agents for the preparation of enol silyl ethers from ketones and aldehydes

Abstract

We have developed an efficient method for the preparation of enol silyl ethers using novel agents, silazanes together with NaH or DBU catalyst, wherein TMS and TBDMS groups were smoothly and chemoselectively introduced into ketones and aldehydes under mild conditions.

Anilinosilanes/TBAF Catalyst: Mild and Powerful Agent for the Silylation of Sterically Hindered Alcohols

“…Silazanes are also efficient silylation agents for alcohols or phenols promoted by the PyH + ·OTf -catalyst, 4 and for ketones or aldehydes giving enol silyl ethers catalyzed by NaH or DBU. 5 Consistent with the study of these mild, catalytic, and practical silylations systems, we report herein a nearly neutral and powerful method utilizing a novel agent, anilinosilanes 1-TBAF catalyst (Scheme 1). The present method covers three types of silylation (TMS, TES, TBS) against sterically uncrowded and crowded alcohols under mild conditions.…”

“…Table 2 lists the results of the silylations (TMS, TES, and TBS) for various alcohols. Not only primary and secondary alcohols, but also sterically crowded tertiary alcohols were successfully silylated in good to excellent isolated yields (entries [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Cl atom, THP and methyl ester functions tolerated the reaction conditions (entries [21][22][23][24][25][26].…”

Practical and robust method for stereoselective preparations of ketene silyl (thio)acetal derivatives and NaOH-catalyzed crossed-Claisen condensation between ketene silyl acetals and methyl esters

“…We previously described the first catalytic base-promoted preparation of enol silyl ethers; NaH functioned for ketones and DBU did for aldehydes (Scheme 1). 2 Recently, a practical and robust method for regio-and stereoselective preparation of (E)-TMS-KSAs and b-ketoester-derived tert-butyl (1Z,3E)-1,3-bis(TMS)dienol ethers was reported (Scheme 2). 3 As a synthetic application of these silyl enolates, methyl and tert-butyl ester-derived KSAs were utilized for the first base-catalyzed crossed-Claisen condensation with simple methyl esters (Scheme 3).…”

Sequential Barium‐Catalysed N−H/H−Si Dehydrogenative Cross‐Couplings: Cyclodisilazanes versus Linear Oligosilazanes

“…Silazanes are common andv ersatile compounds containing NÀ Si bonds which can be used in coordinationc hemistry, [1] as bases, [2] silylating agents [3] or protecting groups for amines,i ndoles and anilines in organic synthesis. [4] Oligo-a nd polysilazanes are commonly prepared by alkali-mediated ring-opening polymerisation of cyclosilazanes following the Seyferth-Wiseman procedure.…”

“…[10] Polycarbosilazanes are commonly synthesisedb ya minolysis of dichlorosilanesw ith 1,2-ethylenediamine [11] or other diamines [12] upon releaseo fa mmonium chlorides as by-products. [13] Nevertheless, until recently,t he most atom-efficient synthetic protocol relied on the cross-dehydrocoupling( CDC) of 1,4-bis(dimethylsilyl)benzene and ammonia catalysed by Pd 2 (dba) 3 ,a na ttractivep rocess even thought he reactionr e-quires7 2h to convert only ap ortion of 200 equiv of the comonomers. [13] Nevertheless, until recently,t he most atom-efficient synthetic protocol relied on the cross-dehydrocoupling( CDC) of 1,4-bis(dimethylsilyl)benzene and ammonia catalysed by Pd 2 (dba) 3 ,a na ttractivep rocess even thought he reactionr e-quires7 2h to convert only ap ortion of 200 equiv of the comonomers.…”