Unusual fragmentation of trimethylsilylated enols derived from m‐ and p‐hydroxyacetophenones

Abstract

When 4hydroxyacetophenone is treated with MSTFA the corresponding his-trimethylsilylated enol ether (la) is obtained. The m a s spectrum of la is characterized by a [M -11' base peak. Extensive deuteration experiments revealed that the hydrogen is mainly removed from a ring position, but originates also to some extent from the side chain (methylidene group) and even to a very small amount from the hydrogens of the methyl groups of the enolic trimethylsilyl group. A mechanism for this fragmentation behaviour is formulated.

Molecular Tectonics. Porous Hydrogen-Bonded Networks Built from Derivatives of Pentaerythrityl Tetraphenyl Ether

“…Similar reactions provided the tetrakis(3,5-disubstituted) derivatives 20 − 22 shown in Table . In the course of this work, we devised new syntheses of 3,5-dibromophenol ( 23 ) and 3,5-diiodophenol ( 24 ) by the routes summarized in Scheme . Derivatives of 4-hydroxybiphenyl could also be used to make pentaerythrityl tetrakis(biphenyl) ethers 25 − 28 (Table ).…”

“…3,5-Dibromophenol (23). A solution of 1,3,5-tribromobenzene (20.0 g, 63.5 mmol) in diethyl ether (300 mL) was stirred at −78 °C under N 2 and treated dropwise with butyllithium (25.4 mL, 2.50 M in hexane, 63.5 mmol). The resulting mixture was kept at −78 °C for 45 min, and then B(OCH 3 ) 3 (10.7 mL, 95.5 mmol) was added dropwise.…”

“…The acidified mixture was extracted twice with CH 2 Cl 2 , and the organic layers were combined and dried over Na 2 SO 4 . Removal of volatiles by evaporation under reduced pressure left a residue of 3,5-dibromophenol ( 23 ; 12.2 g, 48.4 mmol, 76%) as an off-white solid: mp 79 °C (lit 28b. mp 80 °C; lit 28c.…”

Mass Spectrometric Fragmentation of Trimethylsilyl and Related Alkylsilyl Derivatives

“…Showing proposed hydrogen scrambling and loss of an aromatic hydrogen from an enol‐TMS derivative (D = deuterium) (Kraus & Spiteller, ).…”

“…This ion has been shown to involve mainly loss of the hydrogen from a ring position but, in addition, to some extent, from the methylidene group and to a very small extent from the hydrogens of the enolic TMS group. One stage in the proposed mechanism involves exchange of hydrogens between the TMS and methylidene groups ( bx ) as shown in Scheme by use of the d 9 ‐TMS derivative (Kraus & Spiteller, ).…”