Isoxazolo pyrimidines, synthesis

This type of rearrangement can also occur as a consequence of in situ formation of a suitable intermediate, such as in the case of tandem or cascade reactions. Examples of the isoxazole-to-oxazole rearrangement have been studied both computationally and experimentally, providing evidence of the involvement of a 1,2,4-oxadiazole intermediate (2009JOC351). Synthetically useful cascade rearrangements have also been reported for the one-pot synthesis of indazoles (2011SL3018) and a series of isoxazolo-pyrimidines (2011OL4749). 

The dimethoxy isoxazolo[4,5-pyrimidine derivative (96) showed solvent-dependent photochemistry (Scheme 2). Thus, irradiation in ether followed by alkaline hydrolysis gives compound (98) which is believed to be formed via the intermediate (97). The structure of the product (98) was established by synthesis via reductive cleavage of compound (96) to give the imine (99) and subsequent hydrolysis. Photolysis of compound (96) in carbon tetrachloride afforded a mixture of the products (100)-(102) <85JHC156l>. 

X-ray diSraaion, 6, 618 Isoxazolo[5,4-d]pyrimidine applications, 6, 634 synthesis, 6, 54 from isoxazoles, 6, 627 from pyrimidines, 6, 627... 

One synthesis of isoxazolo[5,4-Z>]pyrimidines from 4-unsubtituted 5-AI has been reported (Section III.C.2). As discussed above for isoxazolo[3,4-Z>]pyridines, the reaction of 3-amino-5-methylisoxazole with carbamate 44 does not produce isoxazolo [3,4-7>]pyrimidines, isoxazolo[2,3-a] 1.3.5-triazines 45 being formed as the only products. Meanwhile, the condensation of 5-amino-3-methylisoxazole with the same carbamate yielded isoxazolo[5,4-Z>]pyrimidine 46 (04KGS496) (Scheme 20). 

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