BAMOL

The Rawal group next applied diol catalysis to the enantioselective vinylogous Mukaiyama aldol (VMA) reaction of electron-deficient aldehydes [105]. Screening of various known chiral diol derivatives, including VANOL, VAPOL, BINOL, BAMOL, and TADDOL, revealed that 38a was the only catalyst capable of providing products in acceptable levels ofenantioselection (Scheme 5.55). Subsequent to this work, Scettri reported a similar study of TADDOL-promoted VMA reactions with Chan s diene [106]. 

Scheme 24.12 Asymmetric hetero-Diels-Alder reaction catalysed by BAMOLs 29.

Occasionally, however, a ring methyl group arises from the carboxyl carbon after total reduction, as in the formation of bamol (XXVIII) (Mosbach and Ljungcrantz, 1965) or javanicin (XXIX) (Gatenbeck and Bentley, 1%5). Only the methyl groups marked with an asterisk in these structures are derived from methionine (see also Scheme 2). It should also be remembered that alkylation may occur at nucleophilic positions of aromatic precursors in susceptible products of shikimic acid origin, as in the synthesis, for example, of plastoquinone and ubiquinone (Threlfall et al., 1968). 

Scheme 1.30 Enantioselective hetero Diels-Alder reactions catalyzed by chiral BAMOLs.

Yamamoto and Rawal developed a novel axially chiral l,l -biaryl-2,2 -dimethanol (BAMOL) scaffold (32) (Figure 2.28) as a catalyst for the hetero Diels-Alder... 

Rawal and Yamamoto visualized that axially chiral l,l -biaryl-2,2 -dimethanols (BAMOLs) 25a and 25b possessing the 4-fluoro-3,5-dimethylphenyl and 4-fluoro-3,5-diethylphenyl groups, respectively, could activate the aldehyde carbonyl through hydrogen bonding and thus act as a prominent catalyst for the enantiose-lective hetero-Diels-Alder reaction of an aminosiloxydiene with a wide variety of aldehydes as illustrated in Scheme 7.44 [69]. 

Scheme 10.6 Enantioselective hetero-Diels-Alder reaction catalyzed by BAMOL 5.

A crystal stracture of l,l -biphenyl-BAMOL and benzaldehyde revealed the presence of an intramolecular hydrogen bond between the two hydroxyl groups of the catalyst and an intermolecular hydrogen bond to the carbonyl of benzaldehyde. 

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