Benzyne-Mediated Nonconcerted Pathway toward Synthesis of Sterically Crowded [5]- and [7]Oxahelicenoids, Stereochemical and Theoretical Studies, and Optical Resolution of Helicenoids

Abstract

Synthesis of [5]- and [7]­oxahelicenoids via Diels–Alder reaction of sterically crowded bichromenes with benzyne is presented. Studies carried out on Diels–Alder addition product establish the unusual preference for a stepwise mechanism over the concerted reaction pathway. This high yielding general synthetic protocol affords unexpected anti cycloadducts [5]- and [7]­oxahelicenoids, as confirmed by crystallographic analysis. To rationalize these intriguing antiaddition products, the reaction mechanism was elucidated by means of DFT analysis. Additionally, hydroxy-functionalized [7]­oxahelicenoid has been resolved in its optically pure forms.

o-Silylaryl Triflates: A Journey of Kobayashi Aryne Precursors

“…Subsequently, the same group applied Oppolzer’s sultam as the chiral auxiliary in diastereoselective Diels–Alder reactions between either the pyrrole or furan moiety and o -silylaryl triflates, affording enantiomerically pure benzofused [2.2.1] heterobicycles . Moreover, aryne Diels–Alder reactions with linear dienes were then utilized by various groups. − It is worth mentioning that Vankar and co-workers applied this strategy in the preparation of 1,2-annulated- C -aryl glycosides 4-16 from 1,3-diene 4-15 , the products of which could be further converted to sugar-fused and sugar-branched naphthalenes as well (Scheme b) …”

Directional Approach to Enantiomerically Enriched Functionalized [7]Oxa-helicenoids and Groove-Based Selective Cyanide Sensing

“…Furthermore, their twisted geometry resembling natural biopolymers is an additional alluring factor. In general, helicenes are ortho-fused fully polyaromatic compounds possessing a helical conformation, whereas helicenoids are helicenelike molecules having small partially saturated moieties as a part of their helical π-conjugated framework. Both the types of molecules indeed are used in enantioselective catalysis, , chiral recognition, and development of advanced materials …”

“…Though the reports on helicene synthesis and its applications are abundant, the preparation of enantiopure helicenoids and their applications are sporadically presented. It should be also noted that electronic circular dichroism (ECD) has been widely applied as a detection tool for chiral cation sensing .…”

Synthesis of Derivatised Homoisoflavonoids to Target Ocular Angiogenesis

“…1 Thus, development of a small molecule biologic, such as a homoisoflavonoid, may provide an alternative and less invasive route of drug administration, as well as tackle resistance issues. Though potentially active homoisoflavonoid compounds may be found in nature from plant families such as Asparagaceae, 3 here, we describe the synthesis of and derivatised (E)-3-benzylidene-4-chromanones and 3-benzylchromanes via cyclisation of 3-phenoxypropanenitrile intermediates 4 , 5 which will be evaluated for anti-proliferative activity.…”