A metal- and base-free domino protocol for the synthesis of 1,3-benzoselenazines, 1,3-benzothiazines and related scaffolds

Abstract

Efficient and operationally simple protocols have been demonstrated for the synthesis of the title compounds using easily available starting materials under mild conditions, giving a broad range of rarely reported molecules in excellent yields.

Reagent-Controlled Divergent Synthesis of 2-Amino-1,3-Benzoxazines and 2-Amino-1,3-Benzothiazines

“…Having surveyed the experimental results and literature evidences, ,,,− the plausible mechanism has been presented for the synthesis of 1,3-benzoxazine and 1,3-benzothiazine (Scheme ). The proposed mechanism for the formation of the carbodiimide intermediate E via dehydrosulfurization of intermediate C is well established in the literature. , The mechanism is supported by the isolation of precipitated elemental sulfur .…”

“…Another potential route could be the formation of carbodiimide intermediate E , which delivers the corresponding 1,3-benzoxozine ( 4ab ) (path b). On the other hand, the plausible pathway for the formation of 1,3-benzothiazine can be suggested (Scheme ) based on the literature evidences . The reaction involves the activation of thiourea moiety A by T3P, leading to the formation of intermediate G .…”

“…Therefore, the development of an efficient and easy to access approach for the preparation of 2-amino-1,3-benzoxazines and 2-amino-1,3-benzothiazines could be a useful tool in organic synthesis. On the other hand, T3P (2,4,6-tripropyl-1,3,5,2,4,6-trioxatriphosphorinane-2,4,6-trioxide solution) has been widely employed in both academia and industry as a mild coupling reagent for the synthesis of wide variety of biologically important molecules . It is well documented in the literature that T3P is a choice of reagent in acid–amine coupling reactions because of its ease of handing and robustness.…”

Insights into the Recent Synthetic Advances of Organoselenium Compounds

“…A greener approach, [72] employed a cyclodehydrating reagent, T3P (2,4,6‐Tripropyl‐1,3,5,2,4,6‐trioxatriphosphorinane‐2,4,6‐trioxide solution), to synthesize 1,3‐benzoselenazine scaffold 16 . Addition of T3P (as a solution in ethyl acetate) to a combination of 2‐amino aryl alkyl alcohols 14 and aryl selenocarboxamides 15 , in air at room temperature led to 1,3‐benzoselenazines 16 a – e (Scheme 7).…”

Aza‐Michael addition of 1,2‐diazoles to structurally diverse enones: Efficient methods toward β‐amino ketones

“…After demonstrating considerable substrate scope for the developed reaction conditions, we forged ahead to propose a plausible reaction mechanism for this chemical transformation (Scheme 4). According to the proposed mechanism, [ 12 ] the nucleophilic attack of oxygen atom of enone 1a on to the phosphorus‐atom of T3P ( A ) leading to the formation of intermediate B which may form the corresponding resonance structure B' . Next, the nucleophilic addition of azole 2 on to in situ generated carbocation of enone delivers the intermediate C , which on subsequent hydrolysis and tautomerization provides the desired product 3 .…”