# Supplementary Information (SI) for Organic & Biomolecular Chemistry.
# This journal is © The Royal Society of Chemistry 2026

####################################################################### 
# 
# This file contains crystal structure data downloaded from the 
# Cambridge Structural Database (CSD) hosted by the Cambridge 
# Crystallographic Data Centre (CCDC).
# 
# Full information about CCDC data access policies and citation 
# guidelines are available at http://www.ccdc.cam.ac.uk/access/V1 
# 
# Audit and citation data items may have been added by the CCDC. 
# Please retain this information to preserve the provenance of 
# this file and to allow appropriate attribution of the data. 
# 
#######################################################################

data_shelx
_audit_block_doi                 10.5517/ccdc.csd.cc2kb4nq
_database_code_depnum_ccdc_archive 'CCDC 2363243'
loop_
_audit_author_name
_audit_author_address
'Olga Lodochnikova'
;Arbuzov Institute of Organic and Physical Chemistry
Russia
;
_audit_update_record             
;
2024-06-17 deposited with the CCDC.	2026-05-19 downloaded from the CCDC.
;

_audit_creation_method           SHELXL-2017/1
_shelx_SHELXL_version_number     2017/1
_chemical_name_systematic        
5a,6,6-trimethyltetrahydro-4H,7H-3a,7-methanofuro[3,2-c]benzofuran-2,4(3H)-dione
_chemical_name_common            ?
_chemical_formula_moiety         'C14 H18 O4'
_chemical_formula_sum            'C14 H18 O4'
_exptl_crystal_recrystallization_method 
'recrystallization from petroleum ether. Crystals were grown from ethyl acetate'
_chemical_melting_point          415

_exptl_crystal_description       prism
_exptl_crystal_colour            colorless
_diffrn_ambient_temperature      120(2)
_chemical_formula_weight         250.28

loop_
_atom_type_symbol
_atom_type_description
_atom_type_scat_dispersion_real
_atom_type_scat_dispersion_imag
_atom_type_scat_source
C C 0.0033 0.0016 'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4'
H H 0.0000 0.0000 'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4'
O O 0.0106 0.0060 'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4'

_space_group_crystal_system      monoclinic
_space_group_IT_number           14
_space_group_name_H-M_alt        'P 21/n'
_space_group_name_Hall           '-P 2yn'
_chemical_absolute_configuration ?

loop_
_space_group_symop_operation_xyz
'x, y, z'
'-x+1/2, y+1/2, -z+1/2'
'-x, -y, -z'
'x-1/2, -y-1/2, z-1/2'

_shelx_space_group_comment       
;
The symmetry employed for this shelxl refinement is uniquely defined
by the following loop, which should always be used as a source of
symmetry information in preference to the above space-group names.
They are only intended as comments.
;

_cell_length_a                   7.7918(9)
_cell_length_b                   21.075(3)
_cell_length_c                   7.8390(10)
_cell_angle_alpha                90
_cell_angle_beta                 103.999(4)
_cell_angle_gamma                90
_cell_volume                     1249.0(3)
_cell_formula_units_Z            4
_cell_measurement_temperature    120(2)
_cell_measurement_reflns_used    9849
_cell_measurement_theta_min      2.85
_cell_measurement_theta_max      30.05
_exptl_crystal_density_meas      ?
_exptl_crystal_density_method    ?
_exptl_crystal_density_diffrn    1.331
_exptl_crystal_F_000             536
_exptl_transmission_factor_min   ?
_exptl_transmission_factor_max   ?
_exptl_crystal_size_max          0.668
_exptl_crystal_size_mid          0.594
_exptl_crystal_size_min          0.405
_exptl_absorpt_coefficient_mu    0.097
_shelx_estimated_absorpt_T_min   0.938
_shelx_estimated_absorpt_T_max   0.962
_exptl_absorpt_correction_type   multi-scan
_exptl_absorpt_correction_T_min  0.927
_exptl_absorpt_correction_T_max  0.957
_exptl_absorpt_process_details   SADABS
_exptl_absorpt_special_details   ?
_diffrn_radiation_probe          ?
_diffrn_radiation_type           MoK\a
_diffrn_radiation_wavelength     0.71073
_diffrn_source                   ?
_diffrn_measurement_device_type  'Bruker APEX-II CCD'
_diffrn_measurement_method       'φ and ω scans'
_diffrn_detector_area_resol_mean ?
_diffrn_reflns_number            37532
_diffrn_reflns_av_unetI/netI     0.0220
_diffrn_reflns_av_R_equivalents  0.0553
_diffrn_reflns_limit_h_min       -10
_diffrn_reflns_limit_h_max       10
_diffrn_reflns_limit_k_min       -27
_diffrn_reflns_limit_k_max       27
_diffrn_reflns_limit_l_min       -10
_diffrn_reflns_limit_l_max       10
_diffrn_reflns_theta_min         2.847
_diffrn_reflns_theta_max         27.996
_diffrn_reflns_theta_full        25.242
_diffrn_measured_fraction_theta_max 0.998
_diffrn_measured_fraction_theta_full 0.998
_diffrn_reflns_Laue_measured_fraction_max 0.998
_diffrn_reflns_Laue_measured_fraction_full 0.998
_diffrn_reflns_point_group_measured_fraction_max 0.998
_diffrn_reflns_point_group_measured_fraction_full 0.998
_reflns_number_total             3018
_reflns_number_gt                2780
_reflns_threshold_expression     'I > 2σ(I)'
_reflns_Friedel_coverage         0.000
_reflns_Friedel_fraction_max     .
_reflns_Friedel_fraction_full    .

_reflns_special_details          
;
 Reflections were merged by SHELXL according to the crystal
 class for the calculation of statistics and refinement.
 
 _reflns_Friedel_fraction is defined as the number of unique
 Friedel pairs measured divided by the number that would be
 possible theoretically, ignoring centric projections and
 systematic absences.
;

_computing_data_collection       ?
_computing_cell_refinement       ?
_computing_data_reduction        ?
_computing_structure_solution    'SHELXT 2014/4 (Sheldrick, 2014)'
_computing_structure_refinement  'SHELXL-2017/1 (Sheldrick, 2017)'
_computing_molecular_graphics    ?
_computing_publication_material  ?
_refine_special_details          ?
_refine_ls_structure_factor_coef Fsqd
_refine_ls_matrix_type           full
_refine_ls_weighting_scheme      calc
_refine_ls_weighting_details     
'w=1/[σ²(Fo²)+(0.0605P)²+0.2952P] where P=(Fo²+2Fc²)/3'
_atom_sites_solution_primary     ?
_atom_sites_solution_secondary   ?
_atom_sites_solution_hydrogens   geom
_refine_ls_hydrogen_treatment    constr
_refine_ls_extinction_method     none
_refine_ls_extinction_coef       .
_refine_ls_number_reflns         3018
_refine_ls_number_parameters     166
_refine_ls_number_restraints     0
_refine_ls_R_factor_all          0.0427
_refine_ls_R_factor_gt           0.0401
_refine_ls_wR_factor_ref         0.1086
_refine_ls_wR_factor_gt          0.1068
_refine_ls_goodness_of_fit_ref   1.135
_refine_ls_restrained_S_all      1.135
_refine_ls_shift/su_max          0.001
_refine_ls_shift/su_mean         0.000

loop_
_atom_site_label
_atom_site_type_symbol
_atom_site_fract_x
_atom_site_fract_y
_atom_site_fract_z
_atom_site_U_iso_or_equiv
_atom_site_adp_type
_atom_site_occupancy
_atom_site_site_symmetry_order
_atom_site_calc_flag
_atom_site_refinement_flags_posn
_atom_site_refinement_flags_adp
_atom_site_refinement_flags_occupancy
_atom_site_disorder_assembly
_atom_site_disorder_group
O1 O 0.67807(9) 0.56377(3) 0.49588(9) 0.01659(17) Uani 1 1 d . . . . .
O6 O 0.69560(9) 0.70170(3) 0.47879(9) 0.01754(17) Uani 1 1 d . . . . .
O2 O 0.90002(11) 0.55494(4) 0.36263(10) 0.02288(19) Uani 1 1 d . . . . .
O7 O 0.83048(11) 0.76005(4) 0.31230(11) 0.0264(2) Uani 1 1 d . . . . .
C2 C 0.83835(13) 0.57911(5) 0.47302(13) 0.0156(2) Uani 1 1 d . . . . .
C16 C 0.43839(13) 0.61529(5) 0.57735(14) 0.0203(2) Uani 1 1 d . . . . .
H16A H 0.408147 0.631870 0.456981 0.031 Uiso 1 1 calc R U . . .
H16B H 0.403507 0.646096 0.656351 0.031 Uiso 1 1 calc R U . . .
H16C H 0.375689 0.575220 0.581472 0.031 Uiso 1 1 calc R U . . .
C7 C 0.84062(13) 0.71956(5) 0.42209(13) 0.0184(2) Uani 1 1 d . . . . .
C12 C 1.01949(13) 0.59761(5) 0.77784(13) 0.0171(2) Uani 1 1 d . . . . .
H12A H 1.051021 0.553569 0.753726 0.021 Uiso 1 1 calc R U . . .
H12B H 1.129674 0.620983 0.830941 0.021 Uiso 1 1 calc R U . . .
C3 C 0.92038(12) 0.63031(4) 0.60514(12) 0.0141(2) Uani 1 1 d . . . . .
C8 C 1.00211(13) 0.68169(5) 0.51472(14) 0.0184(2) Uani 1 1 d . . . . .
H8A H 1.063980 0.663414 0.429720 0.022 Uiso 1 1 calc R U . . .
H8B H 1.085979 0.708096 0.600958 0.022 Uiso 1 1 calc R U . . .
C4 C 0.75377(12) 0.66221(4) 0.63481(12) 0.0143(2) Uani 1 1 d . . . . .
C5 C 0.63576(12) 0.60398(4) 0.63485(13) 0.0146(2) Uani 1 1 d . . . . .
C11 C 0.89511(13) 0.59753(5) 0.90469(13) 0.0180(2) Uani 1 1 d . . . . .
H11 H 0.949854 0.571682 1.010903 0.022 Uiso 1 1 calc R U . . .
C15 C 0.71666(14) 0.49837(5) 0.79626(15) 0.0214(2) Uani 1 1 d . . . . .
H15A H 0.745935 0.478131 0.912259 0.032 Uiso 1 1 calc R U . . .
H15B H 0.808002 0.488159 0.733878 0.032 Uiso 1 1 calc R U . . .
H15C H 0.601908 0.482726 0.728534 0.032 Uiso 1 1 calc R U . . .
C9 C 0.78077(14) 0.70416(5) 0.79677(14) 0.0204(2) Uani 1 1 d . . . . .
H9A H 0.664707 0.718467 0.812915 0.024 Uiso 1 1 calc R U . . .
H9B H 0.850253 0.742142 0.781385 0.024 Uiso 1 1 calc R U . . .
C13 C 0.70749(13) 0.57055(5) 0.81838(13) 0.0166(2) Uani 1 1 d . . . . .
C10 C 0.87959(15) 0.66660(5) 0.96013(14) 0.0231(2) Uani 1 1 d . . . . .
H10A H 0.998727 0.684874 1.007054 0.028 Uiso 1 1 calc R U . . .
H10B H 0.813554 0.668775 1.053158 0.028 Uiso 1 1 calc R U . . .
C14 C 0.58239(15) 0.58277(6) 0.93995(15) 0.0239(2) Uani 1 1 d . . . . .
H14A H 0.471929 0.559279 0.896315 0.036 Uiso 1 1 calc R U . . .
H14B H 0.556655 0.628250 0.941548 0.036 Uiso 1 1 calc R U . . .
H14C H 0.639026 0.568539 1.059317 0.036 Uiso 1 1 calc R U . . .


_geom_special_details            
;
 All esds (except the esd in the dihedral angle between two l.s. planes)
 are estimated using the full covariance matrix.  The cell esds are taken
 into account individually in the estimation of esds in distances, angles
 and torsion angles; correlations between esds in cell parameters are only
 used when they are defined by crystal symmetry.  An approximate (isotropic)
 treatment of cell esds is used for estimating esds involving l.s. planes.
;

loop_
_geom_bond_atom_site_label_1
_geom_bond_atom_site_label_2
_geom_bond_distance
_geom_bond_site_symmetry_2
_geom_bond_publ_flag
O1 C2 1.3433(12) . ?
O1 C5 1.4790(11) . ?
O6 C7 1.3634(12) . ?
O6 C4 1.4580(11) . ?
O2 C2 1.2002(12) . ?
O7 C7 1.2009(13) . ?
C2 C3 1.5248(13) . ?
C16 C5 1.5131(13) . ?
C16 H16A 0.9800 . ?
C16 H16B 0.9800 . ?
C16 H16C 0.9800 . ?
C7 C8 1.5184(14) . ?
C12 C11 1.5474(14) . ?
C12 C3 1.5485(13) . ?
C12 H12A 0.9900 . ?
C12 H12B 0.9900 . ?
C3 C8 1.5162(13) . ?
C3 C4 1.5289(13) . ?
C8 H8A 0.9900 . ?
C8 H8B 0.9900 . ?
C4 C9 1.5194(13) . ?
C4 C5 1.5334(13) . ?
C5 C13 1.5778(13) . ?
C11 C10 1.5323(15) . ?
C11 C13 1.5620(14) . ?
C11 H11 1.0000 . ?
C15 C13 1.5347(14) . ?
C15 H15A 0.9800 . ?
C15 H15B 0.9800 . ?
C15 H15C 0.9800 . ?
C9 C10 1.5434(15) . ?
C9 H9A 0.9900 . ?
C9 H9B 0.9900 . ?
C13 C14 1.5407(14) . ?
C10 H10A 0.9900 . ?
C10 H10B 0.9900 . ?
C14 H14A 0.9800 . ?
C14 H14B 0.9800 . ?
C14 H14C 0.9800 . ?

loop_
_geom_angle_atom_site_label_1
_geom_angle_atom_site_label_2
_geom_angle_atom_site_label_3
_geom_angle
_geom_angle_site_symmetry_1
_geom_angle_site_symmetry_3
_geom_angle_publ_flag
C2 O1 C5 109.91(7) . . ?
C7 O6 C4 108.49(7) . . ?
O2 C2 O1 122.78(9) . . ?
O2 C2 C3 127.94(9) . . ?
O1 C2 C3 109.28(8) . . ?
C5 C16 H16A 109.5 . . ?
C5 C16 H16B 109.5 . . ?
H16A C16 H16B 109.5 . . ?
C5 C16 H16C 109.5 . . ?
H16A C16 H16C 109.5 . . ?
H16B C16 H16C 109.5 . . ?
O7 C7 O6 120.92(9) . . ?
O7 C7 C8 128.28(10) . . ?
O6 C7 C8 110.81(8) . . ?
C11 C12 C3 107.76(8) . . ?
C11 C12 H12A 110.2 . . ?
C3 C12 H12A 110.2 . . ?
C11 C12 H12B 110.2 . . ?
C3 C12 H12B 110.2 . . ?
H12A C12 H12B 108.5 . . ?
C8 C3 C2 110.02(8) . . ?
C8 C3 C4 103.01(8) . . ?
C2 C3 C4 100.52(7) . . ?
C8 C3 C12 123.33(8) . . ?
C2 C3 C12 108.51(8) . . ?
C4 C3 C12 108.96(7) . . ?
C3 C8 C7 101.88(8) . . ?
C3 C8 H8A 111.4 . . ?
C7 C8 H8A 111.4 . . ?
C3 C8 H8B 111.4 . . ?
C7 C8 H8B 111.4 . . ?
H8A C8 H8B 109.3 . . ?
O6 C4 C9 108.72(8) . . ?
O6 C4 C3 103.09(7) . . ?
C9 C4 C3 115.59(8) . . ?
O6 C4 C5 113.10(8) . . ?
C9 C4 C5 115.29(8) . . ?
C3 C4 C5 100.34(7) . . ?
O1 C5 C16 105.21(8) . . ?
O1 C5 C4 102.58(7) . . ?
C16 C5 C4 116.11(8) . . ?
O1 C5 C13 108.84(7) . . ?
C16 C5 C13 116.89(8) . . ?
C4 C5 C13 106.10(7) . . ?
C10 C11 C12 106.61(8) . . ?
C10 C11 C13 109.80(8) . . ?
C12 C11 C13 112.84(8) . . ?
C10 C11 H11 109.2 . . ?
C12 C11 H11 109.2 . . ?
C13 C11 H11 109.2 . . ?
C13 C15 H15A 109.5 . . ?
C13 C15 H15B 109.5 . . ?
H15A C15 H15B 109.5 . . ?
C13 C15 H15C 109.5 . . ?
H15A C15 H15C 109.5 . . ?
H15B C15 H15C 109.5 . . ?
C4 C9 C10 109.60(8) . . ?
C4 C9 H9A 109.8 . . ?
C10 C9 H9A 109.8 . . ?
C4 C9 H9B 109.8 . . ?
C10 C9 H9B 109.8 . . ?
H9A C9 H9B 108.2 . . ?
C15 C13 C14 106.81(8) . . ?
C15 C13 C11 110.21(8) . . ?
C14 C13 C11 109.70(8) . . ?
C15 C13 C5 110.82(8) . . ?
C14 C13 C5 110.60(8) . . ?
C11 C13 C5 108.69(8) . . ?
C11 C10 C9 108.03(8) . . ?
C11 C10 H10A 110.1 . . ?
C9 C10 H10A 110.1 . . ?
C11 C10 H10B 110.1 . . ?
C9 C10 H10B 110.1 . . ?
H10A C10 H10B 108.4 . . ?
C13 C14 H14A 109.5 . . ?
C13 C14 H14B 109.5 . . ?
H14A C14 H14B 109.5 . . ?
C13 C14 H14C 109.5 . . ?
H14A C14 H14C 109.5 . . ?
H14B C14 H14C 109.5 . . ?

_refine_diff_density_max         0.486
_refine_diff_density_min         -0.291
_refine_diff_density_rms         0.083

