Amines reaction with oxetanes

Cleavage of small heterocycles. Aziridines, epoxides, -" and oxetanes are opened with amines when catalyzed by Yb(OTf)j. The method has been compared with the pressure reaction."... 

The enantioselective preparation of trans-2,4-disubstituted azetidines 4 by treatment of 3 with methanesulfonyl chloride and triethylamine followed by benzylamine at 45 °C has been reported. A-Arylation of the debenzylated 4 has given 5 in yields of 32-96% by use of rac-Binap and moderate reaction temperatures to suppress racemization of the amines . Azetidines can also be formed from certain oxetanes (see 4.2.3) and from P-Iactams (see 4.3 and 4.6) <99JOC9596>. 

When salt crystals of the aryl 1-phenylcyclopenty 1 ketone carboxylic acid 40 with chiral amines such as (+ )-bomylamine or (—)-1-phenylethylamine were irradiated, the optically active exo- and endo-oxetanes 41 or 42 were formed in low to moderate enantiomeric excesses (Scheme 10) [57]. The formation of the oxetanes is believed to occur through Norrish type 1 cleavage and hydrogen abstraction, producing an alkene and an aldehyde, followed by a Paterno-Buchi reaction within the crystal lattice cage. In contrast, solution photolysis of 40 in acetonitrile afforded product 43 as the only isolable product via a typical Norrish type I a-cleavage followed by radical coupling. 

The a,(3-unsaturated ester (8), aldehyde (9), and nitro (10) compounds participate as electrophiles in a number of useful conjugate addition reactions. Copper-catalyzed addition of Grignard reagents provides access to aryl butanoic acid derivatives substituted with an oxetane (equation 1 in scheme 13.7). The ester, aldehyde, and nitro electrophiles also undergo mild Rh-catalyzed additions of aryl and vinyl boronic acids (equation 2 through equation 4 in scheme 13.7). Interestingly, the unsaturated aldehyde participates readily in an amine conjugate addition to afford oxetane substituted 3-amino-acetaldehyde derivatives. 

For a smooth transition from the previous section, we will continue by discussing the work of Sun and coworkers, who reported their efforts on the application of a new directing group in an organocatalyzed MCR in 2013 [25]. The rarely used oxetane proved to be the ideal hydrogen-bond acceptor that supports the formation of the desired transition state. The previously used ethers already exhibited some desired directing effects and delivered perfect diastereoselectivity (>95 5 dr), but proved ineffective for enantioselectivity (<5% ee). By employing the oxetane, however, the envisioned aza-Diels-Alder reaction proceeded as intended with excellent diastereo (>99 1 dr) and enantioselectivity (99% ee). The proposed transition state of this desymmetrization clarifies the selectivity of the reaction the chiral phosphoric acid allows the amine to approach only from the front face (Scheme 14.10). 

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