1‐Arylfluorenols: Convenient preparation via the ester‐mediated nucleophilic aromatic substitution protocol, facile racemization, and intrinsic chiral induction ability

Abstract

Novel 1-aryl-9H-fluoren-9-ols 1 were conveniently synthesized by using the ester-mediated nucleophilic aromatic substitution on 2,6-dimethoxybenzoate 2 by aryl Grignard reagents as the key step. Racemic 1-phenylfluorenol 1a was converted to the diastereomeric esters 8 of (S)-2Ј-methoxy-1,1Ј-binaphthyl-2-carboxylic acid, which were readily separable by silica-gel column chromatography. Reduction of the optically pure diastereomer (+)-8 with LiAlH 4 accompanied an appreciable racemization to give (+)-1a of 89% ee, which provides the first isolation of an optically active fluorenol of defined enantiomeric purity. Intrinsic chiral induction abilities of the 9-fluorenols 1 were examined in the atrolactic acid synthesis from phenylglyoxylates 9 and methylmagnesium iodide with diastereoselectivity of up to 85% de and the binaphthyl coupling of 1-methoxy-2-naphthoates 11 with 2-methoxy-1-naphthylmagnesium bromide with up to 73% de.

Influence of Steric Hindrance on the Core Geometry and Sulfoxidation Chemistry of Carboxylate-Rich Diiron(II) Complexes

“…Reaction of 2,6-diisopropylphenyl 2,6dimethoxybenzoate with 2,6-dimethylphenyl or mesityl Grignard reagents (2,6-Me 2 PhMgBr and 2,4,6-Me 3 PhMgBr) afforded the monoarylated products, which were then converted into a terphenyl with less sterically demanding aryl Grignard reagents (PhMgBr and 3,5-Me 2 PhBr). 35 The -O 2 CAr Ph,Xyl carboxylate is not accessible by this route because it requires a bulky 2,6-xylyl moiety on one of the terphenyl arms. 35 Therefore, the two synthetic strategies are complementary, allowing the preparation of a variety of asymmetric terphenylcarboxylates.…”

“…35 The -O 2 CAr Ph,Xyl carboxylate is not accessible by this route because it requires a bulky 2,6-xylyl moiety on one of the terphenyl arms. 35 Therefore, the two synthetic strategies are complementary, allowing the preparation of a variety of asymmetric terphenylcarboxylates. Preparation and Crystallographic Analysis of 2, 3, 5, and 6.…”

7-Mesityl-2,2-dimethylindan-1-ol: a novel alcohol which serves as both a chiral auxiliary and a protective group for carboxy functions

“…Recently, we and others have shown that axially chiral 2Јmethoxy-1,1Ј-binaphthyl-2-carboxylic acid is very useful as a chiral auxiliary for enantiomeric resolution of alcohols and amines, as well as for determination of their absolute stereochemistry by HPLC, 1 H NMR or X-ray crystallographic analysis. 5,13 The acid was adopted as a chiral resolving agent for the indanol 11 (Scheme 2). Thus, racemic indanol 11 was treated with (S a )-2Ј-methoxy-1,1Ј-binaphthyl-2-carbonyl chloride to afford a diastereomeric mixture of esters 12, which could be separated well by column chromatography on silica gel.…”

“…After work-up, the crude product was purified by column chromatography on silica gel and elution with hexane-ethyl acetate (9 : 1) to give ester 4 (12.5 g, 97%) as colorless crystals, mp 73. 5 Conversion of ester 4 into acid 6. To a solution of ester 4 (12.5 g, 35.5 mmol) in benzene (125 cm 3 ) was added a solution of mesitylmagnesium bromide, which had been prepared from 2-bromomesitylene (12.9 g, 64.8 mmol) and magnesium turnings (2.51 g) in diethyl ether (125 cm 3 ) and diluted with benzene (125 cm 3 ).…”

“…4 To address this limitation, we recently designed fluoren-9-ols bearing an alkyl and an aryl substituent at the 1-and 8position, respectively, which provide a steric environment quite similar to those offered by the arylcyclohexanols and may pro- tect the carboxy group with the 1-and 8-substituent (b). 5 Although they showed intrinsically high chiral induction ability, their esters were found to readily racemize via the cyclopentadienyl anions under basic conditions. We assumed that a 2,2-dialkyl-7-arylindan-1-ol skeleton would embody similar structural features to the fluorenols but resist racemization (c).…”