3-Chroman amine synthesis

The reduction can also be achieved by utilizing in situ generated BHj THF (from sodium borohydride and boron trifluoride etherate). The scope of this reaction includes the synthesis of novel 3-chroman-amine derivatives (60 equation 33). This stereoselective reaction proceeds via the hydroxylamine intermediate only c/s-2-aryl-3-amino derivatives are obtained. 

The synthesis of some 2,2-spiroannelated chroman-4-ones from o-hydroxyacetophenone and a cycloalkanone in the presence of a secondary amine has been described (78S886). The reaction has also been used to prepare a range of chromanones bearing non-identical or... 

Salicylaldehyde reacts with trimethylsilylketene dithioacetal in the presence of a Lewis acid to form the chroman 502, the product of a deoxygenative divinylation (Equation 208) <2001JOC3924>. This reaction can also be applied to salicylaldimines <2003JOC4947>. Treatment of 3,5-dibromosalicylaldehyde with methyl vinyl ketone (MVK) in the presence of DABCO leads to a chroman-4-ol as the major product <2002J(P1)1318>. A stereoselective one-pot synthesis of vy/z-fused chromans from salicylaldehydes, aromatic amines and cyclic enol ethers is carried out in the... 

Chroman, 4-( p-hydroxyphenyl)-2,2,4-trimethyl-X-ray studies, 3, 622 Chroman, 2-methoxy-synthesis, 3, 806 Chroman, 5-methoxy-synthesis, 3, 778 Chroman, 7-methoxy-synthesis, 3, 778 Chroman, 8-methoxy-acylation, 3, 732 Chroman, 2-methoxy-2-methyl-synthesis, 3, 780 Chroman, 2-methyl-synthesis, 3, 785 Chroman, 5-methyl-reactivity, 3, 732 Chroman, 6-nitro-synthesis, 3, 784 Chroman, 4-phenyl-synthesis, 3, 783 Chroman, thio-metabolism, 1, 241 Chroman, 5,6-thio-2-substituted metabolism, 1, 241 Chromanamines H NMR, 3, 580 Chroman-3-amines conformation, 3, 630 (S) -Chroman-2-carbaldehyde synthesis, 3, 779 Chromancarbaldehydes synthesis, 3, 782 Chroman-4-carbamic add synthesis, 3, 782 (R)-Chroman-2-carboxylic add methyl ester... 

A few other examples are listed in Scheme 49 intramolecular addition of amine giving a good synthesis of (/ )-(-P)-camegine, synthesis of chiral butenolides by carbonation of vinylic carbanions and conjugate additions of cuprates yielding chiral chromans. ... 

SoHman et al. reported the synthesis of 3-triphenylphosphoranylidene-chromanes 117 from Mannich bases 115 of the commercial moUusddde niclosamide and the ciunulated yhdes 2, 82 or 88 [73]. The reaction was carried out in boihng toluene and is thought to proceed by initial addition to give the acyl ylides 116, which then cycHze by the unusual expulsion of a secondary amine, i.e. by nudeophihc attack of the ylidic carbon atom at the benzyhc carbon atom. Intermediates 116 were not isolated. The moUusdddal activities of compounds 117 were found to be about tenfold lower than that of the parent niclosamide (Scheme 25). 

Later, the same group [35] disclosed the synthesis of various potential bioactive chiral functionalized chromanes 222 with high levels of enantio- and diastereoselectivity (up to 76% ee and >20 1 dr) via the rosin-derived tertiary amine-thiourea 221 catalyzed enantioselective FC alkylation/cyclization cascade of 1-naphthol 217 with a variety of p,y-unsaturated a-ketoesters 209 (Scheme 2.32). 

Wang elegantly demonstrated the potentiality of chiral diarylprolinol ether 54 in the synthesis of chromanes 56 via enantioselective Michael-type Friedel-Crafts alkylation/cychzation cascade synthetic sequence between 5a and a,p-unsaturated aldehydes 37a [30a]. Under optimal conditions, moderate diastereoselectivity and high enantioselectivity were obtained. Differently, phenol was found unreactive (Scheme 5.17a). The same team years later documented also the activity of a rosin-derived tertiary amine-thiourea 55 in similar process involving 1- and 2-naphthols and P,y-unsaturated a-ketoesters 25 (Scheme 5.17b) [30b]. A proposed model of the enantiodiscrimi-nating step of the reaction is also provided by the authors (58). 

The main stereoselective MBFTs for the synthesis of spirocyclic acetals or aminals involve the activation of a C-C triple bond to form an intermediate cyclic enol ether. The method disclosed above for the synthesis of a-heteroatom-substituted spirocen-ter (see Section 9.3.3, Scheme 9.18) [34] was next extended by the same authors to the synthesis of spiroacetals. They simply used salicyladehyde as starting aldehyde, but the transformation was not diastereoselective anymore [43]. This problem of stereoselectivity was recently solved by Gong and coworkers, who employed a gold(I)/chiral Brpnsted acid catalysis to do so [44], The chroman spiroacetals were obtained in excellent yields (67-97%) and with high stereoselectivities (up to 95% ee, up to 25 1 dr) (Scheme 9.24). This reaction resulted in the formation of three new single bonds and two stereogenic centers. 

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