Dearomatizing and Derivatizing a Mesityl Group on Boron by One‐Pot Photoisomerization and [4+2] Diels–Alder Addition

Abstract

Boron compounds having a conjugated chelate backbone (N,C‐chelate or C,C‐chelate) and two mesityl substituents on boron have been found to undergo a facile one‐pot transformation/reaction with dienophiles, which leads to the dearomatization of one mesityl ring and its [4+2] Diels–Alder addition with the dienophile. Photochemical activation is the key in this transformation of the aryl ring.

Multistep Photoisomerization of Dimesitylboron-Functionalized Stilbene Analogues

“…Complete spectral assignments are provided in the Supporting Information. Further evidence to support the structural elucidation comes from HRMS and DFT-calculated 1 H and 13 C NMR chemical shifts (also see the Supporting Information).…”

“…These signals exhibit long-range J couplings ( 4 J HH = 1.4 Hz) to CH 3 -7 and CH 3 -9, respectively. In addition, the 13 C chemical shifts of C10, C11, and C3 are consistent with alkyl carbons. The steric geometry of 2b was determined via the cross peaks of H4, H10, and H11 in the NOESY spectra.…”

“…Similar reactions for tricoordinate boron compounds have been reported previously. 12,13 Different from the previously reported Mes 2 B−Ph−p-NMe 2 functionalized compound that has its HOMO mainly on the NMe 2 group and its LUMO delocalized on the whole molecule, 7 Z-2a with only the accepting BMes 2 group has its HOMO mainly on the olefin backbone and its LUMO mainly on the BMes 2 group (see the Supporting Information). Hence, the olefin bond can interact with one of the mesityl rings (acting as an electron rich dienophile) to undergo a Diels− Alder reaction instead of forming trans-4a,4b-dihydrophenanthrene derivatives.…”

Synthesis and stereochemistry of chiral aza-boraspirobifluorenes with tetrahedral boron-stereogenic centers

“…13 Due to the high stability of the B-C bonds, BC 4 boranes exhibit high stereochemical stability. 14 To date, chiral tetrahedral boranes with B-N, [15][16][17][18][19][20][21][22][23][24][25][26][27] B-O, [28][29][30][31] B-H, 32,33 and boron-heteroatom [34][35][36][37] bonds have been synthesized and the stereochemistry of the compounds has been studied extensively. For example, Toyota has reported stable chiral tetrahedral boranes with three B-C bonds and one B-N bond (BC 3 N), and examined the racemization process (Fig.…”