Stereoselective Synthesis of 2H‐Chromans by Reductive Deoxygenation of Differently Substituted 2‐Sulfinylmethylchroman‐2‐ols

Abstract

Good‐to‐excellent diastereoselectivies have been achieved in the synthesis of 2H‐chromans by Et3SiH/TMSOTf reductive deoxygenation of differently substituted 2‐sulfinylmethylchroman‐2‐ols and their methyl ketals. The influence of both electron‐donating and ‐withdrawing substituents on the sulfoxide and on the aromatic dihydobenzopyran core has been studied. SOR1 electron‐donating groups (R1 = pMeOPh and 2‐MeO‐1‐naphthyl) led to a competitive reaction in which the sulfoxide was reduced, thus lowering the yield of the sulfinyl 2H‐chromans. The method allows the presence of different groups on the aromatic dihydrobenzopyran unit. The best results in terms of yield and diastereoselectivity were obtained with 2‐[(p‐tolylsulfinyl)methyl]chroman‐2‐ols. All the results are explained on mechanistic grounds. Synthetic transformations of the enantiopure 2H‐chroman (S,RS)‐21 are reported.

Direct Oxidative Cyclization of 3-Arylpropionic Acids to 3,4-Dihydrocoumarins: Reinvestigation of the Reaction Mechanism

“…92 mg, 57% yield; white solid; the analysis results are consistent with the literature reports. , 1 H NMR (300 MHz, CDCl 3 ) δ 7.10 (dd, J = 6.3, 1.5 Hz, 1H), 7.06–6.96 (m, 2H), 2.98 (t, J = 6.6 Hz, 2H), 2.77 (t, J = 6.6 Hz, 2H), 2.30 (s, 3H); 13 C­{ 1 H} NMR (75 MHz, CDCl 3 ) δ 168.8, 150.3, 129.8, 126.3, 125.5, 123.9, 122.5, 29.3, 23.9, 15.7; GC/MS (EI): m / z (%): 162 (100) [ M + ], 134 (83), 120 (32), 105 (14), 91 (90), 77 (19), 65 (16), 51 (17).…”