Acid‐Induced and Reductive Transfor­mations of Enantiopure 3,6‐Dihydro‐2H‐1,2‐oxazines – Synthesis of Dideoxyamino Carbohydrate Derivatives

Abstract

Acid‐catalyzed transformations of carbohydrate‐derived 3,6‐dihydro‐2H‐1,2‐oxazines such as 1, 5 and 13 provided a set of enantiopure furano‐1,2‐oxazines or pyrano‐1,2‐oxazines. The reaction conditions determined the degree of solvolysis of the compounds. An X‐ray analysis of product 6 revealed an interesting network of hydrogen bonds. Reductive cleavage of the N–O bond of the 1,2‐oxazines either by hydrogen/palladium or by samarium diiodide furnished enantiopure aminofuran and ‐pyran derivatives, e.g. 9 and 11 or compound 16, which can be regarded as protected 4‐amino‐1,4‐dideoxyhex‐3‐ulose or 4‐amino‐1,4‐dideoxyoct‐3‐ulose derivatives. We thus have established a short and stereocontrolled route to amino carbohydrate derivatives with 1,2‐oxazines as crucial relay compounds. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Application of L‐Erythrose‐Derived Nitrones in the Synthesis of Polyhydroxylated Compounds via 3,6‐Dihydro‐2H‐1,2‐oxazine Derivatives

“…Because of the presence of the acetonide moieties in their side chains, 1,2‐oxazines such as syn ‐ 5 or anti ‐ 2 should be ideal candidates for Brønsted‐acid‐mediated transformations. This stereoselective approach to aminosugar derivatives had been explored earlier by our group 2b,14. By the general protocol, with p ‐toluenesulfonyl chloride in methanol as a source of hydrogen chloride, transformation of syn ‐ 5 ( dr = 90:10) furnished bicyclic compound 12 as the only isolated product in an excellent 86 % yield (Scheme ).…”

Highly Substituted Furo[3,4‐d][1,2]oxazines: Gold‐Catalyzed Regiospecific and Diastereoselective 1,3‐Dipolar Cycloaddition of 2‐(1‐Alkynyl)‐2‐alken‐1‐ones with Nitrones

“…The configuration of 5 aa was confirmed by the single-crystal X-ray diffraction analysis. [14] Surprisingly, other commonly used metal catalysts such as Sc(OTf) 3 , Sn(OTf) 2 , Cu(OTf) 2 , Yb(OTf) 3 , Y(OTf) 3 , In-(OTf) 3 , and Ni(ClO 4 ) 2 ·6 H 2 O showed almost no catalytic activity, even at elevated reaction temperatures (40 8C). AgOTf and AuCl 3 also catalyzed this transformation but gave lower product yields.…”

“…The configuration of the cycloadducts derived from acyclic ketones 1 d-i, which may be different from cyclic ketones, was also confirmed by the X-ray crystallographic analysis of 5 da. [14] Notably, the catalyst loading could be reduced to 0.2 mol % without any loss in the yield and diastereoselectivity on a 5 mmol scale reaction (Scheme 2). For example, the reactions of 2 a (5.5 mmol) with 1 a (5.15 mmol) or 1 d (5.0 mmol) was complete within 20 minutes to yield 1.97 grams of 5 aa (97 % yield upon isolation; turnover number is about 500) or 2.01 grams of 5 da (91 % yield upon isolation), respectively.…”

“…The compounds cis-5 aa and cis-5 da were converted into functionalized tetrasubstituted amino alcohol containing furans 6 and 8, respectively, by SmI 2 -mediated reductive cleavage of the NÀO bond. [15] Alternatively, the functionalized 1,2-oxazines 7 and 9 were obtained in moderate yields by treatment of cis-5 aa and cis-5 da, respectively, with cerium(IV) ammonium nitrate (CAN). [16] A plausible stepwise reaction pathway for this gold(I)-catalyzed transformation is depicted in Scheme 5.…”

Reactions of Cycloaliphatic Thioketones and Their Oxo Analogues with Lithiated Methoxyallene: A New Approach to Vinylthiiranes

“…The synthetic utility of diverse 1,2-oxazine derivatives leading to polyfunctionalized compounds of potentially biological significance is well documented. [25] For that reason, cycloadduct 30 was treated with an excess of SmI 2 to give unsaturated amino alcohol 31 in 72 % yield. [26] A surprising resistance of the 3,6-dihydro-1,2-oxazine 30 to undergo exhaustive hydrogenation was observed employing palladium on charcoal as a catalyst.…”